Saline soluble inorganic fibres

ABSTRACT

Disclosed is use of a vitreous inorganic fiber in the knowledge that it has a composition meeting the criterion that the calculated sum of the free energies of hydration of the compounds that would or could be present at equilibrium (on the basis of knowledge, informed belief or reasonable assumption) is more negative than -10 kcal/100 grams of composition. Such compositions are saline soluble.

This is a continuation of application Ser. No. 08/535,587, filed Sep. 28, 1995, now abandoned, which is a continuation of application Ser. No. 08/039,086, filed as application No. PCT/GB/93/00085 filed Jan. 15, 1993, now abandoned.

This invention relates to saline soluble, non-metallic, amorphous, inorganic oxide, refractory fibrous materials.

Inorganic fibrous materials are well known and widely used for many purposes (e.g. as thermal or acoustic insulation in bulk, mat, or blanket form, as vacuum-formed shapes, as vacuum formed boards and papers, and as ropes, yarns or textiles; as a reinforcing fibre for building materials; as a constituent of brake blocks for vehicles). In most of these applications the properties for which inorganic fibrous materials are used require resistance to heat, and often resistance to aggressive chemical environments.

Inorganic fibrous materials can be either glassy or crystalline. Asbestos is an inorganic fibrous material one form of which has been strongly implicated in respiratory disease.

It is still not clear what the causative mechanism is that relates some asbestos with disease but some researchers believe that the mechanism is mechanical and size related. Asbestos of a critical size can pierce cells in the body and so, through long and repeated cell injury, have a bad effect on health.

Whether this mechanism is true or not regulatory agencies have indicated a desire to categorise any inorganic fibre product that has a respiratory fraction as `hazardous`, regardless of whether there is any evidence to support such categorisation. Unfortunately for many of the applications for which inorganic fibres are used, there are no realistic substitutes.

Accordingly there is a demand for inorganic fibres that will pose as little risk as possible (if any) and for which there are objective grounds to believe them safe.

A line of study has proposed that if inorganic fibres were made that were sufficiently soluble in physiological fluids that their residence time in the human body was short; then damage would not occur or at least be minimised. As the risk of asbestos-linked disease appears to depend very much on the length of exposure this idea appears reasonable. Asbestos is extremely insoluble.

As intercellular fluid is saline in nature the importance of fibre solubility in saline solution has long been recognised. If fibres are soluble in physiological saline solution then, provided the dissolved components are not toxic, the fibres should be safer than fibres which are not so soluble. The shorter the time a fibre is resident in the body the less damage it can do. H. Forster in `The behaviour of mineral fibres in physiological solutions` (Proceedings of 1982 WHO IARC Conference, Copenhagen, Volume 2, pages 27-55 (1988)) discussed the behaviour of commercially produced mineral fibres in physiological saline solutions. Fibres of widely varying solubility were discussed.

International Patent Application No. WO87/05007 disclosed that fibres comprising magnesia, silica, calcia and less than 10 wt % alumina are soluble in saline solution. The solubilities of the fibres disclosed were in terms of parts per million of silicon (extracted from the silica-containing material of the fibre) present in a saline solution after 5 hours of exposure. The highest value revealed in the examples had a silicon level of 67 ppm. In contrast, and adjusted to the same regime of measurement, the highest level disclosed in the Forster paper was equivalent to approximately 1 ppm. Conversely if the highest value revealed in the International Patent Application was converted to the same measurement regime as the Forster paper it would have an extraction rate of 901,500 mg Si/kg fibre--i.e. some 69 times higher than any of the fibres Forster tested, and the fibres that had the highest extraction rate in the Forster test were glass fibres which had high alkali contents and so would have a low melting point. This is convincingly better performance even taking into account factors such as differences in test solutions and duration of experiment.

International Patent Application No. WO89/12032 disclosed additional fibres soluble in saline solution and discusses some of the constituents that may be present in such fibres.

European Patent Application No. 0399320 disclosed glass fibres having a high physiological solubility.

Further patent specifications disclosing selection of fibres for their saline solubility are European 0412878 and 0459897, French 2662687 and 2662688, PCT WO86/04807 and WO90/02713.

The refractoriness of the fibres disclosed in these various prior art documents varies considerable. The maximum service temperature of any of these disclosed fibres (when used as refractory insulation) is up to 815° C. (1500° F.).

Service temperature for refractory insulation is definable in many ways but to be consistent with the above mentioned International Patent Applications this application shall mean by service temperature that temperature at which the fibre shows acceptable shrinkage (maximum of 5% linear shrinkage after exposure to temperature for 24 hours) and at which the fibre has not appreciably suffered through excessive sintering or softening.

There is a demand for physiologically soluble fibres having a service temperature of greater than 815° C., particularly for such fibres having a service temperature above 900° C.

Testing for physiological solubility and safety can be done by inhalation studies on, e.g. rats. However such studies are extremely time consuming and costly. A study can take of the order of 21/2 years from start and can easily cost .English Pound.1 million per study. A cheaper alternative is to test for solubility in physiological or like fluids in vitro.

Testing of an inorganic fibre for solubility in physiological solutions is not so time consuming, but there is currently no way of predicting which systems will produce such soluble fibres. Therefore anyone seeking to find such soluble fibres has to work on a trial and error basis assisted by what is commonly known as `chemical intuition` but is equally commonly known as `a hunch`. Such trial and error testing is laborious and time consuming. Further, once a fibre is found that is soluble there is no guarantee that it will be usable at useful service temperatures.

Accordingly there is a demand for a method of predicting whether a fibre will have a reasonable solubility in physiological solutions, and further there is a demand that such a test should preferably give an indication as to expected service temperature.

Shrinkage of inorganic refractory fibres occurs through two mechanisms; the first is viscous flow of the fibre material. Most inorganic refractory fibres are glasses and so may be defined as liquids having an exceedingly high viscosity (but still liable to flow). By their nature fibres are elongate and so have a high surface area per unit volume. As the reduction of surface area is a means of reducing the surface energy of a material, when the glass becomes fluid enough it will flow so as to reduce surface area. This flow results in a coarsening and shortening of the fibres and so to shrinkage, and in the extreme results in disruption of the fibres into separate particles.

The second mechanism leading to shrinkage is that at elevated temperatures glasses may crystallise to form one or more crystal phases. Usually these crystal phases have a smaller molar volume than the glasses from which they crystallise and so shrinkage results. Some fibres are known for which the molar volume of the crystalline form exceeds that of the glass (for example Al₂ O₃ /SiO₂ glassy fibres may crystallise to form mullite crystals). In these cases the expansion due to crystallisation may oppose the shrinkage caused by viscous flow.

If shrinkage through viscous flow occurs at a much lower temperature than crystallisation then the crystallisation may not be able to compensate for such shrinkage.

There is a demand for a fibre in which both viscous flow and crystallisation occur at as high and as similar a temperature as possible, and preferably in which the expansion due to crystallisation closely matches the shrinkage due to viscous flow so that the net effect is as close to zero shrinkage as possible.

When used as refractory insulation inorganic refractory fibres are used in several forms. The fibres may be supplied as a bulk material, but in this form the fibres are difficult to handle for many applications. Alternatively the fibre may be supplied as a blanket. Blanket fibre is generally made by a process of sucking fibre from air onto a conveyor to form a blanket. Because the fibres tend to be aligned parallel to the conveyor surface they can separate easily. Accordingly the blanket fibres are secured together by adding a binder to lock the fibres together, or by needling the blanket, or both. In needling needles are passed through the thickness of the blanket to push and draw fibres to lie transverse to the blanket and so tie the fibres together. Because binders are usually resins, such as phenolic resins, they burn off on first firing. There is a desire to reduce the amount of such binders used both because of possible health implications in handling, and because the combustion products may affect the strength of the fibres. Thus needled blanket is usually preferred.

The fibres may also be supplied as blocks, generally made from assembled layers of inorganic fibre blanket.

For some fibres needling is not possible. Crystalline fibres are generally too brittle to stand the stresses involved. For the fibres known in the industry as glass fibres (which are generally used for low temperature applications) the amount of `shot` (unfiberised glass particles) present is generally too high to allow needling as the shot damages the needles. There is no needled blanket on the market that has a maximum service temperature in the range 900° C.-1200° C. There are needled blankets having a higher maximum service temperature but these use expensive fibres in comparison with other fibres usable (with the aid of binders) as blanket in the temperature range 900° C.-1200° C.

Accordingly there is a demand for needled fibre blanket formed from inexpensive materials, being soluble in saline solutions, and having a maximum service temperature in the range 900° C.-1200° C.

As stated previously refractory oxide fibres are made by several methods all of which involve the formation of a melt of oxides and the subsequent fiberisation of the melt by e.g. spinning or blowing.

The melt of oxide material is often formed by electrical discharge melting of the constituent raw materials. The applicants, in manufacture of a CaO/MgO/SiO₂ refractory oxide fibre encountered problems due to the necessity of handling CaO. These problems were discovered to be due to the moisture content of CaO as commercially available. One of the problems of use of CaO is the outgasing that results upon melting and this led at the least to a porous melt pool which caused fluctuations in the melt current; in the extreme the outgasing was explosive. Additionally use of CaO appeared to cause accelerated attack on the melt electrodes. Also CaO is a difficult and corrosive material to handle.

Accordingly there is a need for a process that minimises the use of CaO.

Accordingly the present invention provides the following features both independently and in combination:

A. Use of a vitreous inorganic fibre in the knowledge that it has a composition meeting the criteria either:--that the calculated sum of the free energies of hydration of the compounds that would or could be present at equilibrium (on the basis of knowledge, informed belief or reasonable assumption) is more negative than -10 kcal/100 grams (-418.4 kJ/kg) of composition; or that the percentage of non-bridging oxygens is more than 30%. Such compositions tend to be saline soluble.

B. Use of such a vitreous inorganic fibre in the knowledge that it has a composition meeting the criterion that the ratio of glass modifiers to network formers is less than a critical value (for SiO₂ based compositions the critical value is 1). Such compositions tend to be glass formers.

C. The invention also encompasses fibres selected by adopting such criteria as a test for solubility and glass formation.

D. Use as saline soluble fibres having a shrinkage of less than 3.5% when exposed to 1000° C. for 24 hours and/or 800° C. for 24 hours, of vitreous fibres having a composition comprising (in weight %):

    ______________________________________                                         SiO.sub.2                                                                              >58%             (for MgO =< 10%) and                                  SiO.sub.2                                                                              >58% + 0.5 (% MgO -10)                                                                          (for MgO >= 10%)                                      (SiO.sub.2 preferably being below 70%)                                         CaO     0%-42%                                                                 MgO     0%-31.33%                                                              Al.sub.2 O.sub.3                                                                       0%-<3.97%                                                              ______________________________________                                    

and being essentially free of fluxing components such as alkali metals and boron oxide.

E. In one such usage the first crystalline material resulting on crystallisation has the crystal structure of diopside and has the composition consisting essentially of:

    ______________________________________                                         Component   Composition A Weight percent                                       ______________________________________                                         SiO.sub.2   59-64                                                              Al.sub.2 O.sub.3                                                                             0-3.5                                                            CaO         19-23                                                              MgO         14-17                                                              ______________________________________                                    

F. In a second such usage the first crystalline material resulting on crystallisation has the crystal structure of wollastonite/pseudowollastonite and has the composition consisting essentially of:

    ______________________________________                                         Component   Composition B Weight percent                                       ______________________________________                                         SiO.sub.2   60-67                                                              Al.sub.2 O.sub.3                                                                             0-3.5                                                            CaO         26-35                                                              MgO         4-6                                                                ______________________________________                                    

G. The fibres used in such manner may further be used as needled blankets.

H. Preferably the fibres of the general composition and compositions A and B mentioned above have a SiO₂ content (expressed as a weight percentage of the constituents SiO₂, CaO and MgO) of greater than 60%.

I. The present invention further provides a method for the manufacture of refractory oxide fibres containing calcium and silicon by the formation of an oxide melt containing calcium and silicon characterised in that all or part of the calcium and all or part of silicon is provided by a calcium silicate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example in the following description and with reference to the drawings in which:

FIG. 1 is a three-axis phase diagram indicating the crystalline phases in the system SiO₂ /CaO/MgO (Phase Diagrams for Ceramists, The American Ceramic Society, 1964) a key to this diagram is at the end of the specification;

FIG. 2 is a three-axis composition plot of the projection onto the SiO₂ /CaO/MgO phase field of compositions comprising SiO₂, CaO, MgO and Al₂ O₃ ;

FIG. 3 is a temperature/time plot of the firing regime used in a series of cyclic exposure tests of experimental compositions;

FIG. 4 is a plot of log (total solubility) v calculated free energy of hydration for a series of fibres.

FIG. 5 is a plot of log (total solubility) v % non-bonding oxygens for a series of fibres (see below).

A series of fibres were made of the compositions shown in Table 1. These fibres were melt spun by using a vertical spinning system of the type known for making inorganic fibres. Also shown in Table 1 are the compositions of some comparative commercially available inorganic oxide fibres and glass fibres.

                  TABLE 1                                                          ______________________________________                                               Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                              CaO  MgO   ZrO.sub.2                                     ______________________________________                                         SW-A   3.3    59.2    20.5 15.5  --                                            SW-A1  1.1    63.7    20.5 15.2  --                                            SW-A2  0.8    60.8    21.4 15.4  --                                            SW-B1  2.3    65.3    26.8  5.7  --                                            SW-B2  1.3    66.9    27.5  5.2  --                                            SW-B3  1.0    60.0    34.0  4.4  --                                            ______________________________________                                         COMPARATIVE EXAMPLES                                                                 Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                              CaO  MgO   ZrO.sub.2                                                                           MST                                      ______________________________________                                         CRBT  46.5    53       0.04                                                                                0.01 --   1260° C.                          CWBT  40.6    49.5     5.50                                                                                4.00 --    870° C.                          CHBT  49.7    35.1     0.04                                                                                0.01 14.7 1425° C.                          Glass 15.2/   53.7/   21.1/                                                                                1.3/ --   + 5.9-6.2% B.sub.2 O.sub.3               Fibre 15.5    57.5    21.8  1.6          0.11-0.12% TiO.sub.2                                                           0.46% Na.sub.2 O                                                               0.32-0.33% K.sub.2 O                  Needled                                                                               3.7    60.5/    8.1  4.0  --   + 2.85-2.95% B.sub.2 O.sub.3             Glass         60.0     7.9       --      13.5% Na.sub.2 O                      Fibre                                    1.0% K.sub.2 O                        ______________________________________                                          [MST = Maximum Service Temperature (oxidising atmosphere)                

The fibres SW-A, SW-A1, SW-A2, SW-B1, SW-B2 and SW-B3 were tested for solubility by the following method.

The fibre was first chopped in the following manner. 2.5 g of fibre (deshotted by hand) was liquidised with 250 cm³ of distilled water in a domestic Moulinex (Trade Mark) food blender for 20 seconds. The suspension was then transferred to a 500 cm³ plastic beaker and allowed to settle after which as much liquid as possible was decanted and the remaining liquid removed by drying in an oven at 110° C.

The solubility test apparatus comprised a shaking incubator water bath, and the test solution had the following composition:

    ______________________________________                                         Compound      Name             Grams                                           ______________________________________                                         NaCl          Sodium chloride  6.780                                           NH.sub.4 Cl   Ammonium chloride                                                                               0.540                                           NaHCO.sub.3   Sodium bicarbonate                                                                              2.270                                           Na.sub.2 HPO.sub.4.H.sub.2 O                                                                 Disodium hydrogen phosphate                                                                     0.170                                           Na.sub.3 C.sub.6 H.sub.5 O.sub.7P.2H.sub.2 O                                                 Sodium citrate dihydrate                                                                        0.060                                           H.sub.2 NCH.sub.2 CO.sub.2 H                                                                 Glycine          0.450                                           H.sub.2 SO.sub.4 s.g. 1.84                                                                   Sulphuric acid   0.050                                           ______________________________________                                    

The above materials were diluted to 1 litre with distilled water to form a physiological-like saline solution.

0.500 grams±0.0003 grams of chopped fibre was weighed into a plastic centrifuge tube and 25 cm³ of the above saline solution added. The fibre and saline solution was shaken well and inserted into the shaking incubator water bath maintained at body temperature 37° C.±1° C.). The shaker speed was set at 20 cycles/minute.

After the desired period (usually 5 hours or 24 hours) the centrifuge tube was removed and centrifuged at ≈4500 revs/minute for approximately 5 minutes. Supernatant liquid was then drawn off using a syringe and hypodermic needle. The needle was then removed from the syringe, air expelled from the syringe, and the liquid passed through a filter (0.45 micron cellulose nitrate membrane filter paper [WCN type from Whatman Labsales Limited]) into a clean plastic bottle. The liquid was then analysed by atomic absorption using a Thermo Jarrell Ash Smith--Hiefje II machine.

The operating conditions were:

    ______________________________________                                                                              FLAME                                                                          (Nitrous                                          WAVELENGTH  BAND     CURRENT Oxide +                                   ELEMENT (nm)        WIDTH    (MA)    Acetylene)                                ______________________________________                                         Al      309.3       1.0      8       Fuel Rich                                 SiO.sub.2                                                                              251.6       0.3      12      "                                         CaO     422.7       1.0      7       Fuel Lean                                 MgO     285.2       1.0      3       "                                         ______________________________________                                    

The procedure and standards adopted for determining the above elements were as set out below.

SiO₂ can be determined without dilution up to 250 ppm concentration (1 ppm≡1 mg/Litre). Above this concentration an appropriate dilution was made volumetrically. A 0.1% KCl solution (0.1 g in 100 cm³) was added to the final dilution to prevent ionic interference. NB If glass apparatus is used, prompt analysis is necessary.

From a stock solution of 1000 ppm pure ignited silica (99.999%) (fused with Na₂ CO₃ at 1200° C. for 20 minutes in a platinum crucible (0.2500 g SiO₂ /2 g Na₂ CO₃) and dissolved in dilute hydrochloric acid (4 molar) made up to 250 cm³ with distilled water in a plastic volumetric flask) the following standards were produced:

    ______________________________________                                         STANDARD (PPM SiO.sub.2)                                                                       STOCK SOLUTION (cm.sup.3)                                      ______________________________________                                         10.0            1.0                                                            20.0            2.0                                                            30.0            3.0                                                            50.0            5.0                                                            100.0           10.0                                                           250.0           25.0                                                           ______________________________________                                    

Aluminium may be measured directly from the sample without dilution. Standards of 1.0, 5.0 and 10.0 ppm Al may be used. For calibration readings are multiplied by 1.8895 to convert from Al to Al₂ O₃.

A standard Al atomic absorption solution (e.g. BDH 1000 ppm Al) was bought and diluted using an accurate pipette to the desired concentration. 0.1% KCl was added to prevent ionic interference.

Calcium may require dilutions on the sample before determination can be carried out (i.e. ×10 and ×20 dilutions). Dilutions must contain 0.1% KCl.

A standard Ca atomic absorption solution (e.g. BDH 1000 ppm Ca) was diluted with distilled water and an accurate pipette to give standards of 0.5, 4.0 and 10.0 ppm. 0.1% KCl is added to prevent ionic interference. To convert readings obtained from Ca to CaO a factor of 1.4 was used.

Magnesium may require dilutions on the sample before determinations can be made (i.e. ×10 and ×20). Add 0.1% KCl to each dilution. To convert Mg to MgO multiply by 1.658.

A standard Mg atomic absorption solution (e.g. BDH 1000 ppm Mg) was diluted with distilled water and an accurate pipette to give standards of 0.5, 1.0 and 10.0 ppm Mg. 0.1% KCl was added to prevent ionic interference.

All stock solutions were stored in plastic bottles.

The results of the tests are indicated in Table 2.

                  TABLE 2                                                          ______________________________________                                         BODY FLUIDS SOLUBILITY (ppm)                                                          SiO.sub.2     CaO         MgO                                                  5 h  24 h     5 h   24 h  5 h   24 h                                    ______________________________________                                         SW-A     98     120      63  56    33    66                                    SW-A1    83     141      32  70    21    70                                    SW-A2    130    202      43  73    100   177                                   SW-B1    58      77      10  38    5      9                                    SW-B2    64     121      27  55    5     10                                    SW-B3    138    192      80  46    8     21                                    ______________________________________                                    

Fibres with the best solubility (SW-A2 and SW-B3) were then tested, after annealing at varying temperatures, and compared with the comparative examples of Table 1. The results are shown in Table 3.

It can be seen that for the SW-A2 fibre, with increasing annealing temperature, the silica solubility drops progressively. In contrast the SW-B3 composition shows no loss in solubility up to 800° C. and although a reduction in solubility is shown above that temperature it is not as dramatic as for SW-A2. Despite this difference in solubility it is to be noted that only the needled GF fibre shows a comparable silica solubility and that material melts at 700° C.

                                      TABLE 3                                      __________________________________________________________________________                     Solubility Analyses                                                            CaO (ppm)                                                                             MgO (ppm)                                                                             SiO.sub.2 (ppm)                                  Fibre   Condition                                                                              5 hrs                                                                             24 hrs                                                                             5 hrs                                                                             24 hrs                                                                             5 hrs                                                                             24 hrs                                        __________________________________________________________________________     SW-A2   As received                                                                            58 37  37 3   89 130                                           SW-A2   600° C., 48 hrs                                                                 33 56  27 43  60 108                                           SW-A2   800° C., 48 hrs                                                                 35 53  17 30  43 87                                            SW-A2   1000° C., 48 hrs                                                                 7  3  3  2   11 21                                            SW-B3   As received                                                                            35 69  7  22  22 100                                           SW-B3   600° C., 48 hrs                                                                 61 150 12 22  55 130                                           SW-B3   800° C., 48 hrs                                                                 41 90  3  7   24 144                                           SW-B3   1000° C., 48 hrs                                                                18 40  3  3   17 60                                            CRBT    As received                                                                            10  8  6  3    5 3                                             CHBT    As received                                                                            16 10  7  3    4 0.3                                           Glass Fibre                                                                            As received                                                                            14 17  5  3    5 7                                             Needled GF                                                                             As received                                                                            17 34  8  15  66 85                                            Needled GF                                                                             600° C., 48 hrs                                                                 11 26  7  10  19 37                                            Mineral Fibre                                                                          As received                                                                            16 16  7  6    8 9                                             __________________________________________________________________________      [The Glass Fibre and Needled Glass Fibre had the compositions shown in         Table 1.                                                                 

The user is primarily concerned with the solubility of the fibre as received as it is in this condition that most handling occurs; as received both SW-A2 and SW-B3 fibres have extremely high solubility. Even after exposure to 800° C. and 1000° C. these fibres have solubilities much higher than other high temperature use fibres.

To investigate the reasons underlying the difference in solubilities after high temperature annealing between the SWA-2 and SW-B3 fibres qualitative X-ray diffraction was done on the fibres. The results are indicated in Table 4 and it can be seen that the SW-B3 fibre forms pseudowollastonite and wollastonite, whereas the SW-A2 fibre forms diopside. It appears therefore that the crystalline diopside has a lower solubility in physiological saline solution than the crystalline pseudowollastonite and wollastonite material precipitated from the SW-B3 fibre.

                  TABLE 4                                                          ______________________________________                                         Sample Condition    Qualitative XRD                                            ______________________________________                                         SW-A2   600° C., 48 hours                                                                   Amorphous                                                  SW-A2   800° C., 48 hours                                                                   Amorphous with small amount Diopside                       SW-A2  1000° C., 48 hours                                                                   Diopside                                                   SW-B3   600° C., 48 hours                                                                   Amorphous                                                  SW-B3   800° C., 48 hours                                                                   Amorphous                                                  SW-B3  1000° C., 48 hours                                                                   Pseudowollastonite & Wollastonite                          ______________________________________                                    

Various of the fibres were then tested for their shrinkage characteristics. Table 5 shows the results of Shrinkage tests on all the test fibres and on some of the comparative fibres. These results were obtained by proposed ISO standard ISO/TC33/SC2/N220 (equivalent to British Standard BS 1920, part 6,1986) with some modifications to account for sample size. The method in summary comprises the manufacture of vacuum cast preforms, using 75 g of fibre in 500 cm³ of 0.2% starch solution, into a 120×65 mm tool. Platinum pins (approx 0.1-0.3 mm diameter) were placed 100×45 mm apart in the 4 corners. The longest lengths (L1 & L2) and the diagonals (L3 & L4) were measured to an accuracy of ±0.01 mm using a travelling microscope attached to a steel rule with a vernier scale. The samples were placed in a furnace at temperature and left for 24 hours. The shrinkage values are given as an average of the 4 measurements.

                  TABLE 5                                                          ______________________________________                                         LINEAR SHRINKAGE (%) (24 h at temperature)                                     Temp. ° C.                                                                       SW-A    SW-A1   SW-A2 SW-B1 SW-B2 SW-B3                               ______________________________________                                          730     1.45            1.43  1.02  0.22                                       870                           0.41                                             900                     1.07              1.07                                1000             1.04    1.3   0.51  0.6   1.1                                 1100             0.71    1.8         0.73  2.2                                 Maximum  850     1050    1050  1050  1050  1000                                Service                                                                        Temperature                                                                    ° C.                                                                    ______________________________________                                    

It can be seen that in SW-A, SW-A1, SW-A2, SW-B1, SW-B2 and SW-B3, owing to the increase in molar volume on crystillisation, the linear shrinkage at the maximum service temperature is less than 3.5%.

Table 6 shows the results of a further series of shrinkage tests made in the same way.

                  TABLE 6                                                          ______________________________________                                         Measurement                                                                    Direction      Test        Linear                                              c.f. Roll      Temperatures                                                                               Shrinkages %                                        Sample Direction   ° C. Range  Mean                                     ______________________________________                                         SW-A2  Parallel     850        1.1-1.4                                                                               1.2                                      SW-A2  Perpendicular                                                                               850        0.7-1.5                                                                               1.3                                      SW-A2  Parallel     900        0.5-1.1                                                                               0.9                                      SW-A2  Perpendicular                                                                               900        1.9-4.5                                                                               3.0                                      SW-A2  Parallel    1000        0.5-2.9                                                                               1.3                                      SW-A2  Perpendicular                                                                              1000        1.7-2.9                                                                               2.2                                      SW-A2  Parallel    1100        0.7-1.5                                                                               1.0                                      SW-A2  Perpendicular                                                                              1100        1.0-2.6                                                                               1.8                                      SW-B3  Parallel     900        1.6-1.8                                                                               1.7                                      SW-B3  Perpendicular                                                                               900        1.4-2.4                                                                               2.1                                      SW-B3  Parallel    1000        1.6-2.3                                                                               1.9                                      SW-B3  Perpendicular                                                                              1000        1.0-2.3                                                                               1.7                                      SW-B3  Parallel and                                                                               1100        Complete Melting                                       Perpendicular           (Lantern type                                                                  remnant)                                        ______________________________________                                    

To ascertain the applicability of these tests to long term usage a series of cyclic shrinkage tests were undertaken on the materials and the heating schedule used for these cyclic tests is shown in FIG. 3.

The results of the tests are shown in Tables 7 & 8 (the two figures given for SW-B3 are due to slight differences in chemical analysis [the fibre at the end of a production run of fibre tends to have slightly differing composition to that at the beginning of a production run of fibre]).

As a further comparison with the above discussed materials a melt was made comprising 55% SiO₂, 29.9% CaO and 18.6% MgO. Fibres made using this composition had a maximum service temperature of 700° C. and melted at 800° C.

As these results were encouraging the applicants conducted a further and extensive series of tests, concentrating on the SW-A2 and SW-B3 compositions, to ascertain the reproducibility of these results and the boundaries of the useful compositions.

Table 9 (three pages) below gives the compositions of a series of melts, ranked on silica content, and showing the shrinkage figure after exposure to 1000° C. for 24 hours (1st column) and 800° C. for 24 hours (2nd column). These shrinkages were measured by the same method as the shrinkages given above but measurements were made with a travelling microscope with a digital linear scale accurate to ±5 μm. It can clearly be seen that all fibres with a silica content of less than 58% have a shrinkage at 1000° C. of greater than 3.5% save two (B3-3 and 708). These fibres, together with some fibres with a silica content of greater than 58% although showing a reasonable figure at 1000° C., show a very poor figure at 800° C. Compositions with an SiO₂ content of greater than 70% appear to fiberise poorly. This may be because such compositions have two liquids in the melt as may be appreciated from FIG. 1

                  TABLE 7                                                          ______________________________________                                         CYCLIC SHRINKAGE (LINEAR) (%)                                                  Product  1000° C.                                                                            1100° C.                                                                         24 h at 1000° C.                          ______________________________________                                         No. cycles                                                                              58          42                                                        CRBT     2.0         2.7      1.9                                              CWBT     15.0        13.3     12.1                                             SW-A2    0.33        2.0      1.3                                              SW-B3    1.00        1.67     1.1                                              SW-B3    0.33        0.67     1.1                                              ______________________________________                                          Accuracy: + or - 0.33%                                                   

                  TABLE 8                                                          ______________________________________                                         CYCLIC SHRINKAGE (%)                                                           LINEAR SHRINKAGE       THICKNESS                                                               24 h at                                                                               SHRINKAGE                                               PRODUCT 1000° C.                                                                         1100° C.                                                                         1000° C.                                                                       1000° C.                                                                       1100° C.                        ______________________________________                                         No. cycles                                                                             104      100             104    100                                    CRBT    1.47     3.1      1.9    0.47   11.19                                  CWBT    14.4     15.2     12.1   38.63  32.14                                  SW-A2   1.5      2.1      1.3    8.58   8.75                                   SW-B3   1.73     1.63     1.1    7.24   7.57                                   SW-B3   1.47     1.77     1.1    7.02   7.16                                   ______________________________________                                          Accuracy: + or - 0.3% (%)                                                

                                      TABLE 9                                      __________________________________________________________________________                                           Shrinkage                                Analysed Compositions (Weight %)      at ° C.                                                                       Rationalised Compositions          Melt                                                                               SiO.sub.2 %                                                                        CaO %                                                                              MgO %                                                                              Al.sub.2 O.sub.3 %                                                                  Na.sub.2 O %                                                                       K.sub.2 O %                                                                        Fe.sub.2 O.sub.3 %                                                                  ZrO.sub.2 %                                                                        1000                                                                              800                                                                               SiO.sub.2 %                                                                        CaO %                                                                              MgO                        __________________________________________________________________________                                                         %                          A2-28                                                                              78.07                                                                              2.07                                                                               17.15                                                                              0.15 <0.05                                                                              <0.05                                                                              0.11 1.76                                                                               ¶                                                                          80.3                                                                               2.1 17.6                       A2-16                                                                              73.43                                                                              12.40                                                                              10.09                                                                              0.19 <0.05                                                                              <0.05                                                                              0.11 2.23                                                                               0.7                                                                                 *                                                                               76.6                                                                               12.9                                                                               10.5                       A2-32                                                                              73.09                                                                              6.36                                                                               19.60                                                                              0.23 0.05                                                                               <0.05                                                                              0.11 0.36                                                                               ¶                                                                          73.8                                                                               6.4 19.8                       B3-32                                                                              72.38                                                                              23.43                                                                              0.65                                                                               0.31 0.31                                                                               0.09                                                                               0.22 0.72                                                                               ¶                                                                          75.0                                                                               24.3                                                                               0.7                        A2-15                                                                              72.25                                                                              12.67                                                                              12.35                                                                              0.11 <0.05                                                                              <0.05                                                                              0.10 1.24                                                                               1.1                                                                                 *                                                                               74.3                                                                               13.0                                                                               12.7                       A2-22                                                                              71.48                                                                              9.36                                                                               16.34                                                                              0.33 0.10                                                                               <0.05                                                                              0.20 0.83                                                                               1.1                                                                               *  73.6                                                                               9.6 16.8                       A2-29                                                                              71.24                                                                              4.46                                                                               22.31                                                                              0.19 <0.05                                                                              <0.05                                                                              0.13 1.23                                                                               1.8                                                                               *1.5                                                                              72.7                                                                               4.5 22.8                       A2-27                                                                              71.14                                                                              6.77                                                                               19.64                                                                              0.24 0.08                                                                               <0.05                                                                              0.13 1.01                                                                               1.2                                                                               *1.2                                                                              72.9                                                                               7.0 20.1                       B3-28                                                                              70.81                                                                              18.74                                                                              7.03                                                                               0.47 0.23                                                                               0.07                                                                               0.16 0.75                                                                               0.2                                                                                 *                                                                               73.3                                                                               19.4                                                                               7.3                        A2-17                                                                              70.43                                                                              11.58                                                                              14.52                                                                              0.15 <0.05                                                                              <0.05                                                                              0.13 1.58                                                                               1.3                                                                                 *                                                                               73.0                                                                               12.0                                                                               15.0                       A2-33                                                                              70.04                                                                              4.61                                                                               22.85                                                                              0.25 0.11                                                                               <0.05                                                                              0.12 1.01                                                                               ¶                                                                          71.9                                                                               4.7 23.4                       B3-18                                                                              69.42                                                                              23.27                                                                              3.76                                                                               0.43 0.37                                                                               0.06                                                                               0.12 0.47                                                                               0.4   72.0                                                                               24.1                                                                               3.9                        A2-6                                                                               69.29                                                                              15.17                                                                              12.76                                                                              0.07 0.25                                                                               <0.05                                                                              0.11 1.13                                                                               1.5   71.3                                                                               15.6                                                                               13.1                       B3-16                                                                              68.74                                                                              24.99                                                                              1.71                                                                               0.65 0.38                                                                               0.10                                                                               0.24 1.03                                                                               0.3                                                                               0.2                                                                               72.0                                                                               26.2                                                                               1.8                        A2-26                                                                              68.65                                                                              8.12                                                                               19.26                                                                              0.29 <0.05                                                                              <0.05                                                                              0.21 0.98                                                                               1.5                                                                               1.5                                                                               71.5                                                                               8.4 20.1                       B3-27                                                                              68.56                                                                              20.98                                                                              7.00                                                                               0.78 0.35                                                                               0.08                                                                               0.17 0.79                                                                               0.8                                                                               0.7                                                                               71.0                                                                               21.7                                                                               7.3                        759 68.33                                                                              17.45                                                                              12.60                                                                              <0.05                                                                               0.11                                                                               <0.05                                                                              0.33 <0.05                                                                              1.7                                                                               1.1                                                                               69.5                                                                               17.7                                                                               12.8                       A2-20                                                                              68.19                                                                              11.58                                                                              16.57                                                                              0.40 0.19                                                                               0.05                                                                               0.21 0.91                                                                               1.1                                                                               1.0                                                                               70.8                                                                               12.0                                                                               17.2                       A2-31                                                                              67.62                                                                              8.45                                                                               21.72                                                                              0.32 0.09                                                                               <0.05                                                                              0.15 0.64                                                                               2.3                                                                               1.9                                                                               69.2                                                                               8.6 22.2                       B3-31                                                                              67.59                                                                              27.76                                                                              0.49                                                                               0.40 0.40                                                                               0.11                                                                               0.22 1.01                                                                               0.7   70.5                                                                               29.0                                                                               0.5                        B3-19                                                                              67.58                                                                              24.91                                                                              3.65                                                                               0.45 0.37                                                                               0.07                                                                               0.15 0.65                                                                               0.5   70.3                                                                               25.9                                                                               3.8                        B3-17                                                                              67.25                                                                              26.68                                                                              1.86                                                                               0.70 0.45                                                                               0.10                                                                               0.23 0.57                                                                               0.3   70.2                                                                               27.9                                                                               1.9                        A2-13                                                                              66.67                                                                              14.87                                                                              16.01                                                                              0.11 0.05                                                                               <0.05                                                                              0.10 0.92                                                                               1.6   68.4                                                                               15.2                                                                               16.4                       B3-22                                                                              66.17                                                                              21.28                                                                              9.34                                                                               0.52 0.33                                                                               0.08                                                                               0.18 0.54                                                                               1.1                                                                               0.8                                                                               68.4                                                                               22.0                                                                               9.6                        A2-10                                                                              66.17                                                                              16.22                                                                              15.80                                                                              0.49 0.06                                                                               <0.05                                                                              0.09 <0.05                                                                              2.2                                                                               1.9                                                                               67.4                                                                               16.5                                                                               16.1                       B3-15                                                                              65.86                                                                              29.82                                                                              1.78                                                                               0.47 0.45                                                                               0.08                                                                               0.18 0.51                                                                               0.3   67.6                                                                               30.6                                                                               1.8                        719 65.77                                                                              25.69                                                                              8.12                                                                               <0.05                                                                               0.24                                                                               <0.05                                                                              0.23 <0.05                                                                              0.5   66.0                                                                               25.8                                                                               8.2                        A2-5                                                                               65.69                                                                              18.74                                                                              13.78                                                                              0.18 0.16                                                                               <0.05                                                                              0.10 0.14                                                                               1.9                                                                               1.0                                                                               66.9                                                                               19.1                                                                               14.0                       B3-4A                                                                              65.50                                                                              25.81                                                                              4.88                                                                               2.05 0.28                                                                               0.12                                                                               0.16 0.24                                                                               1.4                                                                               1.0                                   A2-8                                                                               65.33                                                                              16.86                                                                              14.24                                                                              0.22 0.13                                                                               <0.05                                                                              0.14 1.17                                                                               1.5   67.7                                                                               17.5                                                                               14.8                       718 65.23                                                                              27.14                                                                              6.95                                                                               <0.05                                                                               0.24                                                                               <0.05                                                                              0.20 0.49                                                                               0.4   65.7                                                                               27.3                                                                               7.0                        B3-14                                                                              65.11                                                                              24.91                                                                              5.54                                                                               0.58 0.43                                                                               0.09                                                                               0.19 0.61                                                                               1.0   68.1                                                                               26.1                                                                               5.8                        721 65.08                                                                              27.26                                                                              5.33                                                                               0.06 0.17                                                                               <0.05                                                                              0.08 <0.05                                                                              0.3                                                                               0.6                                                                               66.6                                                                               27.9                                                                               5.5                        A2-34                                                                              64.85                                                                              6.63                                                                               26.20                                                                              0.23 0.06                                                                               <0.05                                                                              0.16 0.80                                                                               3.4                                                                               3.9                                                                               66.4                                                                               6.8 26.8                       A2-21                                                                              64.16                                                                              13.74                                                                              19.98                                                                              0.34 0.17                                                                               <0.05                                                                              0.11 0.13                                                                               3.2                                                                               3.3                                                                               65.6                                                                               14.0                                                                               20.4                       B3-30                                                                              64.13                                                                              31.93                                                                              0.37                                                                               0.64 0.45                                                                               0.09                                                                               0.14 0.28                                                                               0.6   66.5                                                                               33.1                                                                               0.4                        A2-35                                                                              64.12                                                                              8.88                                                                               24.88                                                                              0.29 0.10                                                                               <0.05                                                                              0.13 0.47                                                                               7.3                                                                               7.1                                                                               65.5                                                                               9.1 25.4                       B3-23                                                                              64.09                                                                              23.26                                                                              9.33                                                                               0.56 0.36                                                                               0.09                                                                               0.16 0.30                                                                               1.0   66.3                                                                               24.0                                                                               9.7                        B3-5A                                                                              63.74                                                                              25.41                                                                              4.68                                                                               3.97 0.26                                                                               0.12                                                                               0.17 0.58                                                                               7.4                                                                               4.3                                   A2-30                                                                              63.68                                                                              16.06                                                                              18.21                                                                              0.40 0.11                                                                               0.07                                                                               0.15 <0.05                                                                              2.7                                                                               1.6                                                                               65.0                                                                               16.4                                                                               18.6                       A2-9                                                                               63.66                                                                              21.44                                                                              12.96                                                                              1.49 0.32                                                                               0.10                                                                               0.11 <0.05                                                                              1.9                                                                               0.9                                                                               64.9                                                                               21.9                                                                               13.2                       A2-12                                                                              63.56                                                                              16.55                                                                              18.00                                                                              0.33 0.11                                                                               <0.05                                                                              0.08 0.05                                                                               1.0                                                                               2.3                                                                               64.8                                                                               16.9                                                                               18.3                       B3-6A                                                                              63.24                                                                              24.83                                                                              4.59                                                                               5.70 0.27                                                                               0.11                                                                               0.15 0.15                                                                               21.6                                                                              18.8                                  723 62.61                                                                              29.79                                                                              5.44                                                                               <0.05                                                                               0.17                                                                               <0.05                                                                              0.13 <0.05                                                                              0.4                                                                               0.5                                                                               64.0                                                                               30.4                                                                               5.6                        757 62.60                                                                              20.92                                                                              15.22                                                                              0.20 <0.05                                                                              <0.05                                                                              0.16 <0.05                                                                              1.3                                                                               2.9                                                                               63.4                                                                               21.2                                                                               15.4                       A2-25                                                                              62.36                                                                              10.99                                                                              24.18                                                                              0.33 0.10                                                                               0.05                                                                               0.16 0.07                                                                               6.1   63.9                                                                               11.3                                                                               24.8                       B3-13                                                                              62.33                                                                              30.62                                                                              2.06                                                                               0.55 0.65                                                                               0.09                                                                               0.17 0.91                                                                               0.8                                                                               0.9                                                                               65.6                                                                               32.2                                                                               2.2                        A2-7                                                                               61.98                                                                              23.37                                                                              11.98                                                                              0.44 0.25                                                                               <0.05                                                                              0.10 0.23                                                                               1.4   63.7                                                                               24.0                                                                               12.3                       725 61.83                                                                              28.13                                                                              7.54                                                                               0.10 0.36                                                                               <0.05                                                                              0.17 <0.05                                                                              0.6   63.4                                                                               28.9                                                                               7.7                        B3-11                                                                              61.71                                                                              33.25                                                                              2.33                                                                               0.69 0.52                                                                               0.12                                                                               0.25 0.59                                                                               0.9   63.4                                                                               34.2                                                                               2.4                        B3-24                                                                              61.62                                                                              25.53                                                                              9.73                                                                               0.58 0.38                                                                               0.10                                                                               0.17 <0.05                                                                              1.8                                                                               1.2                                                                               63.6                                                                               26.4                                                                               10.0                       A2-24                                                                              61.38                                                                              13.62                                                                              22.74                                                                              0.31 0.16                                                                               <0.05                                                                              0.14 0.08                                                                               3.3                                                                               12.3                                                                              62.8                                                                               13.9                                                                               23.3                       722 61.33                                                                              31.08                                                                              5.25                                                                               0.05 0.20                                                                               <0.05                                                                              0.16 <0.05                                                                              1.3   62.8                                                                               31.8                                                                               5.4                        924 61.32                                                                              19.78                                                                              14.54                                                                              2.57 <0.05                                                                              <0.05                                                                              0.09 0.66                                                                               0.3                                                                               3.0                                                                               64.1                                                                               20.7                                                                               15.2                       B3-2A                                                                              60.83                                                                              32.30                                                                              0.48                                                                               4.15 0.35                                                                               0.15                                                                               0.19 0.12                                                                               7.5                                                                               3.3                                   A2-14                                                                              60.74                                                                              25.30                                                                              11.66                                                                              0.28 0.18                                                                               0.05                                                                               0.13 0.16                                                                               1.8   62.2                                                                               25.9                                                                               11.9                       B3-1A                                                                              60.32                                                                              32.27                                                                              3.99                                                                               1.74 0.32                                                                               0.10                                                                               0.15 0.09                                                                               2.5                                                                               1.7                                   A2-11                                                                              60.32                                                                              24.28                                                                              13.24                                                                              0.25 0.18                                                                               <0.05                                                                              0.09 0.08                                                                               1.8                                                                               1.1                                                                               61.7                                                                               24.8                                                                               13.5                       B3-9                                                                               60.28                                                                              34.49                                                                              2.50                                                                               0.76 0.50                                                                               0.13                                                                               0.28 0.49                                                                               1.6                                                                               1.7                                                                               62.0                                                                               35.4                                                                               2.6                        A2-23                                                                              60.20                                                                              18.59                                                                              18.78                                                                              0.48 0.19                                                                               0.08                                                                               0.15 0.05                                                                               18.9                                                                              10.7                                                                              61.7                                                                               19.1                                                                               19.2                       B3-1                                                                               60.11                                                                              32.56                                                                              3.80                                                                               0.79 0.54                                                                               0.12                                                                               0.23 0.82                                                                               0.5   62.3                                                                               33.8                                                                               3.9                        932 59.85                                                                              21.60                                                                              15.65                                                                              1.50 0.06                                                                               <0.05                                                                              0.18 0.11                                                                               12.8  61.6                                                                               22.3                                                                               16.1                       692 59.82                                                                              34.34                                                                              5.44                                                                               0.13 0.19                                                                               <0.05                                                                              0.08 0.17                                                                               2.1   60.0                                                                               34.5                                                                               5.5                        B3-3A                                                                              59.54                                                                              31.64                                                                              0.67                                                                               5.91 0.33                                                                               0.15                                                                               0.21 0.41                                                                               43.3                                                                              15.3                                  B3-25                                                                              59.53                                                                              28.15                                                                              9.22                                                                               0.48 0.39                                                                               0.08                                                                               0.14 <0.05                                                                              2.3   61.4                                                                               29.1                                                                               9.5                        B3-29                                                                              59.40                                                                              36.00                                                                              0.68                                                                               0.92 0.43                                                                               0.14                                                                               0.23 0.17                                                                               0.9   61.8                                                                               37.5                                                                               0.7                        714 59.05                                                                              32.00                                                                              8.27                                                                               <0.05                                                                               0.27                                                                               <0.05                                                                              0.40 <0.05                                                                              0.7                                                                               1.2                                                                               59.5                                                                               32.2                                                                               8.3                        696 58.81                                                                              30.91                                                                              6.15                                                                               0.21 0.18                                                                               <0.05                                                                              0.08 0.24                                                                               0.3                                                                               1.4                                                                               61.3                                                                               32.3                                                                               6.4                        A2-19                                                                              58.71                                                                              18.48                                                                              19.74                                                                              0.54 0.20                                                                               0.07                                                                               0.19 <0.05                                                                              4.7   60.6                                                                               19.0                                                                               20.4                       586 58.65                                                                              35.03                                                                              3.90                                                                               0.13 0.23                                                                               <0.05                                                                              0.16 <0.05                                                                              1.9                                                                               1.6                                                                               60.1                                                                               35.9                                                                               4.0                        694 58.39                                                                              33.10                                                                              6.02                                                                               0.27 0.20                                                                               <0.05                                                                              0.10 0.17                                                                               1.6                                                                               1.9                                                                               59.9                                                                               33.9                                                                               6.2                        765 57.78                                                                              3.90                                                                               35.07                                                                              2.12 <0.05                                                                              <0.05                                                                              0.23 <0.05                                                                              34.2  59.7                                                                               4.0 36.3                       660 57.74                                                                              34.65                                                                              4.83                                                                               1.15 0.24                                                                               <0.05                                                                              0.19 <0.05                                                                              24.7  59.4                                                                               35.6                                                                               5.0                        B3-20                                                                              57.57                                                                              32.70                                                                              6.07                                                                               0.91 0.57                                                                               0.13                                                                               0.22 <0.05                                                                              30.9  59.8                                                                               33.9                                                                               6.3                        712 57.54                                                                              35.39                                                                              4.61                                                                               0.06 0.23                                                                               <0.05                                                                              0.12 <0.05                                                                              4.4                                                                               3.4                                                                               59.0                                                                               36.3                                                                               4.7                        B3-21                                                                              57.38                                                                              36.62                                                                              2.43                                                                               0.73 0.51                                                                               0.11                                                                               0.16 0.08                                                                               30.3  59.5                                                                               38.0                                                                               2.5                        B3-26                                                                              56.98                                                                              30.50                                                                              9.44                                                                               0.62 0.44                                                                               0.11                                                                               <0.05                                                                               <0.05                                                                              39.8                                                                              26.6                                                                              58.8                                                                               31.5                                                                               9.7                        A2-18                                                                              56.96                                                                              26.29                                                                              13.01                                                                              0.66 0.51                                                                               0.10                                                                               0.19 <0.05                                                                              36.2  59.2                                                                               27.3                                                                               13.5                       971 56.82                                                                              23.92                                                                              17.36                                                                              0.74 0.18                                                                               <0.05                                                                              0.14 0.05                                                                               41.7  57.9                                                                               24.4                                                                               17.7                       734 56.58                                                                              23.62                                                                              17.05                                                                              1.00 0.06                                                                               <0.05                                                                              0.13 0.05                                                                               39.3  58.2                                                                               24.3                                                                               17.5                       973 56.18                                                                              24.45                                                                              16.81                                                                              0.50 0.08                                                                               <0.05                                                                              0.14 0.05                                                                               34.9  57.7                                                                               25.1                                                                               17.2                       B3-3                                                                               55.99                                                                              36.07                                                                              4.44                                                                               0.58 0.45                                                                               0.09                                                                               0.38 1.46                                                                               0.3                                                                               34.7                                                                              58.0                                                                               37.4                                                                               4.6                        708 55.22                                                                              42.79                                                                              0.77                                                                               <0.05                                                                               0.31                                                                               <0.05                                                                              0.12 <0.05                                                                              1.1                                                                               8.7                                                                               55.9                                                                               43.3                                                                               0.8                        71  54.68                                                                              24.04                                                                              19.66                                                                              0.20 0.17                                                                               <0.05                                                                              0.23 <0.05                                                                              51.7  55.6                                                                               24.4                                                                               20.0                       __________________________________________________________________________      *Poor fibres containing a lot of shot. All other constituents <0.1%.           ¶Too poor to test for solubility or shrinkage                  

                                      TABLE 10                                     __________________________________________________________________________     Analysed Compositions (Weight %)      Solubilities ppm                                                                           Rationalised                                                                   Compositions                 Melt                                                                               SiO.sub.2 %                                                                        CaO %                                                                              MgO %                                                                              Al.sub.2 O.sub.3 %                                                                  Na.sub.2 O %                                                                       K.sub.2 O %                                                                        Fe.sub.2 O.sub.3 %                                                                  ZrO.sub.2 %                                                                        SiO.sub.2                                                                          CaO MgO SiO.sub.2                                                                          CaO                                                                                MgO                  __________________________________________________________________________                                                               %                    A2-28                                                                              78.07                                                                              2.07                                                                               17.15                                                                              0.15 <0.05                                                                              <0.05                                                                              0.11 1.76                                                                               ¶ 80.3                                                                               2.1 17.6                 A2-16                                                                              73.43                                                                              12.40                                                                              10.09                                                                              0.19 <0.05                                                                              <0.05                                                                              0.11 2.23                                                                               113 45  55  76.6                                                                               12.9                                                                               10.5                 A2-32                                                                              73.09                                                                              6.36                                                                               19.60                                                                              0.23 0.05                                                                               <0.05                                                                              0.11 0.36                                                                               ¶ 73.8                                                                               6.4 19.8                 B3-32                                                                              72.38                                                                              23.43                                                                              0.65                                                                               0.31 0.31                                                                               0.09                                                                               0.22 0.72                                                                               ¶ 75.0                                                                               24.3                                                                               0.7                  A2-15                                                                              72.25                                                                              12.67                                                                              12.35                                                                              0.11 <0.05                                                                              <0.05                                                                              0.10 1.24                                                                               105 35  48  74.3                                                                               13.0                                                                               12.7                 A2-22                                                                              71.48                                                                              9.36                                                                               16.34                                                                              0.33 0.10                                                                               <0.05                                                                              0.20 0.83                                                                               126 36  75  73.6                                                                               9.6 16.8                 A2-29                                                                              71.24                                                                              4.46                                                                               22.31                                                                              0.19 <0.05                                                                              <0.05                                                                              0.13 1.23                                                                                94 21  105 72.7                                                                               4.5 22.8                 A2-27                                                                              71.14                                                                              6.77                                                                               19.64                                                                              0.24 0.08                                                                               <0.05                                                                              0.13 1.01                                                                               101 24  67  72.9                                                                               7.0 20.1                 B3-28                                                                              70.81                                                                              18.74                                                                              7.03                                                                               0.47 0.23                                                                               0.07                                                                               0.16 0.75                                                                               108 49  31  73.3                                                                               19.4                                                                               7.3                  A2-17                                                                              70.43                                                                              11.58                                                                              14.52                                                                              0.15 <0.05                                                                              <0.05                                                                              0.13 1.58                                                                                91 35  72  73.0                                                                               12.0                                                                               15.0                 A2-33                                                                              70.04                                                                              4.61                                                                               22.85                                                                              0.25 0.11                                                                               <0.05                                                                              0.12 1.01                                                                               ¶ 71.9                                                                               4.7 23.4                 B3-18                                                                              69.42                                                                              23.27                                                                              3.76                                                                               0.43 0.37                                                                               0.06                                                                               0.12 0.47                                                                               145 66  17  72.0                                                                               24.1                                                                               3.9                  A2-6                                                                               69.29                                                                              15.17                                                                              12.76                                                                              0.07 0.25                                                                               <0.05                                                                              0.11 1.13                                                                               152 48  70  71.3                                                                               15.6                                                                               13.1                 B3-16                                                                              68.74                                                                              24.99                                                                              1.71                                                                               0.65 0.38                                                                               0.10                                                                               0.24 1.03                                                                               132 72  10  72.0                                                                               26.2                                                                               1.8                  A2-26                                                                              68.65                                                                              8.12                                                                               19.26                                                                              0.29 <0.05                                                                              <0.05                                                                              0.21 0.98                                                                               183 31  97  71.5                                                                               8.4 20.1                 B3-27                                                                              68.56                                                                              20.98                                                                              7.00                                                                               0.78 0.35                                                                               0.08                                                                               0.17 0.79                                                                               122 54  20  71.0                                                                               21.7                                                                               7.3                  759 68.33                                                                              17.45                                                                              12.60                                                                              <0.05                                                                               0.11                                                                               <0.05                                                                              0.33 <0.05                                                                              117 38  40  69.5                                                                               17.7                                                                               12.8                 A2-20                                                                              68.19                                                                              11.58                                                                              16.57                                                                              0.40 0.19                                                                               0.05                                                                               0.21 0.91                                                                               162 31  69  70.8                                                                               12.0                                                                               17.2                 A2-31                                                                              67.62                                                                              8.45                                                                               21.72                                                                              0.32 0.09                                                                               <0.05                                                                              0.15 0.64                                                                               103 26  72  69.2                                                                               8.6 22.2                 B3-31                                                                              67.59                                                                              27.76                                                                              0.49                                                                               0.40 0.40                                                                               0.11                                                                               0.22 1.01                                                                               112 50   4  70.5                                                                               29.0                                                                               0.5                  B3-19                                                                              67.58                                                                              24.91                                                                              3.65                                                                               0.45 0.37                                                                               0.07                                                                               0.15 0.65                                                                               163 44  21  70.3                                                                               25.9                                                                               3.8                  B3-17                                                                              67.25                                                                              26.68                                                                              1.86                                                                               0.70 0.45                                                                               0.10                                                                               0.23 0.57                                                                               162 49  13  70.2                                                                               27.9                                                                               1.9                  A2-13                                                                              66.67                                                                              14.87                                                                              16.01                                                                              0.11 0.05                                                                               <0.05                                                                              0.10 0.92                                                                               159 47  70  68.4                                                                               15.2                                                                               16.4                 A2-10                                                                              66.17                                                                              16.22                                                                              15.80                                                                              0.49 0.06                                                                               <0.05                                                                              0.09 <0.05                                                                              122 42  52  67.4                                                                               16.5                                                                               16.1                 B3-22                                                                              66.17                                                                              21.28                                                                              9.34                                                                               0.52 0.33                                                                               0.08                                                                               0.18 0.54                                                                               174 62  57  68.4                                                                               22.0                                                                               9.6                  B3-15                                                                              65.86                                                                              29.82                                                                              1.78                                                                               0.47 0.45                                                                               0.08                                                                               0.18 0.51                                                                               156 38   7  67.6                                                                               30.6                                                                               1.8                  719 65.77                                                                              25.69                                                                              8.12                                                                               <0.05                                                                               0.24                                                                               <0.05                                                                              0.23 <0.05                                                                              115 51  24  66.0                                                                               25.8                                                                               8.2                  A2-5                                                                               65.69                                                                              18.74                                                                              13.78                                                                              0.18 0.16                                                                               <0.05                                                                              0.10 0.14                                                                               150 48  60  66.9                                                                               19.1                                                                               14.0                 B3-4A                                                                              65.50                                                                              25.81                                                                              4.88                                                                               2.05 0.28                                                                               0.12                                                                               0.16 0.24                                                                                82 52  16                               A2-8                                                                               65.33                                                                              16.86                                                                              14.24                                                                              0.22 0.13                                                                               <0.05                                                                              0.14 1.17                                                                               181 54  84  67.7                                                                               17.5                                                                               14.8                 718 65.23                                                                              27.14                                                                              6.95                                                                               <0.05                                                                               0.24                                                                               <0.05                                                                              0.20 0.49                                                                               107 47  20  65.7                                                                               27.3                                                                               7.0                  B3-14                                                                              65.11                                                                              24.91                                                                              5.54                                                                               0.58 0.43                                                                               0.09                                                                               0.19 0.61                                                                               158 67  27  68.1                                                                               26.1                                                                               5.8                  721 65.08                                                                              27.26                                                                              5.33                                                                               0.06 0.17                                                                               <0.05                                                                              0.08 <0.05                                                                              153 68  20  66.6                                                                               27.9                                                                               5.5                  A2-34                                                                              64.85                                                                              6.63                                                                               26.20                                                                              0.23 0.06                                                                               <0.05                                                                              0.16 0.80                                                                                39 11  119 66.4                                                                               6.8 26.8                 A2-21                                                                              64.16                                                                              13.74                                                                              19.98                                                                              0.34 0.17                                                                               <0.05                                                                              0.11 0.13                                                                               160 28  56  65.6                                                                               14.0                                                                               20.4                 B3-30                                                                              64.13                                                                              31.93                                                                              0.37                                                                               0.64 0.45                                                                               0.09                                                                               0.14 0.28                                                                               163 83   3  66.5                                                                               33.1                                                                               0.4                  A2-35                                                                              64.12                                                                              8.88                                                                               24.88                                                                              0.29 0.10                                                                               <0.05                                                                              0.13 0.47                                                                                61 18  106 65.5                                                                               9.1 25.4                 B3-23                                                                              64.09                                                                              23.26                                                                              9.33                                                                               0.56 0.36                                                                               0.09                                                                               0.16 0.30                                                                               101 44  31  66.3                                                                               24.0                                                                               9.7                  B3-5A                                                                              63.74                                                                              25.41                                                                              4.68                                                                               3.97 0.26                                                                               0.12                                                                               0.17 0.58                                                                                48 43  11                               A2-30                                                                              63.68                                                                              16.06                                                                              18.21                                                                              0.40 0.11                                                                               0.07                                                                               0.15 <0.05                                                                              102 33  52  65.0                                                                               16.4                                                                               18.6                 A2-9                                                                               63.66                                                                              21.44                                                                              12.96                                                                              1.49 0.32                                                                               0.10                                                                               0.11 <0.05                                                                              195 67  66  64.9                                                                               21.9                                                                               13.2                 A2-12                                                                              63.56                                                                              16.55                                                                              18.00                                                                              0.33 0.11                                                                               <0.05                                                                              0.08 0.05                                                                               160 47  66  64.8                                                                               16.9                                                                               18.3                 B3-6A                                                                              63.24                                                                              24.83                                                                              4.59                                                                               5.70 0.27                                                                               0.11                                                                               0.15 0.15                                                                                26  7  26                               723 62.61                                                                              29.79                                                                              5.44                                                                               <0.05                                                                               0.17                                                                               <0.05                                                                              0.13 <0.05                                                                              141 62  17  64.0                                                                               30.4                                                                               5.6                  757 62.60                                                                              20.92                                                                              15.22                                                                              0.20 <0.05                                                                              <0.05                                                                              0.16 <0.05                                                                              187 62  73  63.4                                                                               21.2                                                                               15.4                 A2-25                                                                              62.36                                                                              10.99                                                                              24.18                                                                              0.33 0.10                                                                               0.05                                                                               0.16 0.07                                                                               160 35  105 63.9                                                                               11.3                                                                               24.8                 B3-13                                                                              62.33                                                                              30.62                                                                              2.06                                                                               0.55 0.65                                                                               0.09                                                                               0.17 0.91                                                                               151 41   7  65.6                                                                               32.2                                                                               2.2                  A2-7                                                                               61.98                                                                              23.37                                                                              11.98                                                                              0.44 0.25                                                                               <0.05                                                                              0.10 0.23                                                                               178 59  63  63.7                                                                               24.0                                                                               12.3                 725 61.83                                                                              28.13                                                                              7.54                                                                               0.10 0.36                                                                               <0.05                                                                              0.17 <0.05                                                                              186 76  35  63.4                                                                               28.9                                                                               7.7                  B3-11                                                                              61.71                                                                              33.25                                                                              2.33                                                                               0.69 0.52                                                                               0.12                                                                               0.25 0.59                                                                               162 28  15  63.4                                                                               34.2                                                                               2.4                  B3-24                                                                              61.62                                                                              25.53                                                                              9.73                                                                               0.58 0.38                                                                               0.10                                                                               0.17 <0.05                                                                              185 37  57  63.6                                                                               26.4                                                                               10.0                 A2-24                                                                              61.38                                                                              13.62                                                                              22.74                                                                              0.31 0.16                                                                               <0.05                                                                              0.14 0.08                                                                               136 27  87  62.8                                                                               13.9                                                                               23.3                 722 61.33                                                                              31.08                                                                              5.25                                                                               0.05 0.20                                                                               <0.05                                                                              0.16 <0.05                                                                              185 81  23  62.8                                                                               31.8                                                                               5.4                  924 61.32                                                                              19.78                                                                              14.54                                                                              2.57 <0.05                                                                              <0.05                                                                              0.09 0.66                                                                                77 36  37  64.1                                                                               20.7                                                                               15.2                 B3-2A                                                                              60.83                                                                              32.30                                                                              0.48                                                                               4.15 0.35                                                                               0.15                                                                               0.19 0.12                                                                                58 61   5                               A2-14                                                                              60.74                                                                              25.30                                                                              11.66                                                                              0.28 0.18                                                                               0.05                                                                               0.13 0.16                                                                               127 57  43  62.2                                                                               25.9                                                                               11.9                 B3-1A                                                                              60.32                                                                              32.27                                                                              3.99                                                                               1.74 0.32                                                                               0.10                                                                               0.15 0.09                                                                               119 72  16                               A2-11                                                                              60.32                                                                              24.28                                                                              13.24                                                                              0.25 0.18                                                                               <0.05                                                                              0.09 0.08                                                                               149 54  51  61.7                                                                               24.8                                                                               13.5                 B3-9                                                                               60.28                                                                              34.49                                                                              2.50                                                                               0.76 0.50                                                                               0.13                                                                               0.28 0.49                                                                               175  8   5  62.0                                                                               35.4                                                                               2.6                  A2-23                                                                              60.20                                                                              18.59                                                                              18.78                                                                              0.48 0.19                                                                               0.08                                                                               0.15 0.05                                                                               192 35  47  61.7                                                                               19.1                                                                               19.2                 B3-1                                                                               60.11                                                                              32.56                                                                              3.80                                                                               0.79 0.54                                                                               0.12                                                                               0.23 0.82                                                                               146 84  17  62.3                                                                               33.8                                                                               3.9                  932 59.85                                                                              21.60                                                                              15.65                                                                              1.50 0.06                                                                               <0.05                                                                              0.18 0.11                                                                                92 41  43  61.6                                                                               22.3                                                                               16.1                 692 59.82                                                                              34.34                                                                              5.44                                                                               0.13 0.19                                                                               <0.05                                                                              0.08 0.17                                                                               140 67  23  60.0                                                                               34.5                                                                               5.5                  B3-3A                                                                              59.54                                                                              31.64                                                                              0.67                                                                               5.91 0.33                                                                               0.15                                                                               0.21 0.41                                                                                30 25  10                               B3-25                                                                              59.53                                                                              28.15                                                                              9.22                                                                               0.48 0.39                                                                               0.08                                                                               0.14 <0.05                                                                              133 48  33  61.4                                                                               29.1                                                                               9.5                  B3-29                                                                              59.40                                                                              36.00                                                                              0.68                                                                               0.92 0.43                                                                               0.14                                                                               0.23 0.17                                                                               201 29   5  61.8                                                                               37.5                                                                               0.7                  714 59.05                                                                              32.00                                                                              8.27                                                                               <0.05                                                                               0.27                                                                               <0.05                                                                              0.40 <0.05                                                                              142 73  30  59.5                                                                               32.2                                                                               8.3                  696 58.81                                                                              30.91                                                                              6.15                                                                               0.21 0.18                                                                               <0.05                                                                              0.08 0.24                                                                               163 48  37  61.3                                                                               32.3                                                                               6.4                  A2-19                                                                              58.71                                                                              18.48                                                                              19.74                                                                              0.54 0.20                                                                               0.07                                                                               0.19 <0.05                                                                              125 42  66  60.6                                                                               19.0                                                                               20.4                 586 58.65                                                                              35.03                                                                              3.90                                                                               0.13 0.23                                                                               <0.05                                                                              0.16 <0.05                                                                              182 54  19  60.1                                                                               35.9                                                                               4.0                  694 58.39                                                                              33.10                                                                              6.02                                                                               0.27 0.20                                                                               <0.05                                                                              0.10 0.17                                                                               133 66  27  59.9                                                                               33.9                                                                               6.2                  765 57.78                                                                              3.90                                                                               35.07                                                                              2.12 <0.05                                                                              <0.05                                                                              0.23 <0.05                                                                              100 16  169 59.7                                                                               4.0 36.3                 660 57.74                                                                              34.65                                                                              4.83                                                                               1.15 0.24                                                                               <0.05                                                                              0.19 <0.05                                                                              152 69  23  59.4                                                                               35.6                                                                               5.0                  B3-20                                                                              57.57                                                                              32.70                                                                              6.07                                                                               0.91 0.57                                                                               0.13                                                                               0.22 <0.05                                                                              181 29  40  59.8                                                                               33.9                                                                               6.3                  712 57.54                                                                              35.39                                                                              4.61                                                                               0.06 0.23                                                                               <0.05                                                                              0.12 <0.05                                                                              160 24  22  59.0                                                                               36.3                                                                               4.7                  B3-21                                                                              57.38                                                                              36.62                                                                              2.43                                                                               0.73 0.51                                                                               0.11                                                                               0.16 0.08                                                                               175 25  16  59.5                                                                               38.0                                                                               2.5                  B3-26                                                                              56.98                                                                              30.50                                                                              9.44                                                                               0.62 0.44                                                                               0.11                                                                               <0.05                                                                               <0.05                                                                              149 64  41  58.8                                                                               31.5                                                                               9.7                  A2-18                                                                              56.96                                                                              26.29                                                                              13.01                                                                              0.66 0.51                                                                               0.10                                                                               0.19 <0.05                                                                              161 47  57  59.2                                                                               27.3                                                                               13.5                 971 56.82                                                                              23.92                                                                              17.36                                                                              0.74 0.18                                                                               <0.05                                                                              0.14 0.05                                                                               142 55  73  57.9                                                                               24.4                                                                               17.7                 734 56.58                                                                              23.62                                                                              17.05                                                                              1.00 0.06                                                                               <0.05                                                                              0.13 0.05                                                                               135 52  66  58.2                                                                               24.3                                                                               17.5                 973 56.18                                                                              24.45                                                                              16.81                                                                              0.50 0.08                                                                               <0.05                                                                              0.14 0.05                                                                               102 42  47  57.7                                                                               25.1                                                                               17.2                 B3-3                                                                               55.99                                                                              36.07                                                                              4.44                                                                               0.58 0.45                                                                               0.09                                                                               0.38 1.46                                                                               185 14  18  58.0                                                                               37.4                                                                               4.6                  708 55.22                                                                              42.79                                                                              0.77                                                                               <0.05                                                                               0.31                                                                               <0.05                                                                              0.12 <0.05                                                                              193 31   2  55.9                                                                               43.3                                                                               0.8                  71  54.68                                                                              24.04                                                                              19.66                                                                              0.20 0.17                                                                               <0.05                                                                              0.23 <0.05                                                                              133 55  62  55.6                                                                               24.4                                                                               20.0                 __________________________________________________________________________

There are several anomalies, namely compositions B3-6A, A2-25, A2-24, A2-23, B3-2A, B3-3A, A2-19, and 932. All of these have an SiO₂ content of >58% but a high shrinkage.

On the assumption that the minimum silica level for satisfactory shrinkage varies with MgO content the applicants have determined that Libres with a silica content (in weight percent) that fail to meet the following expression do not have satisfactory shrinkages at either or both 800° C. and 1000° C:

    ______________________________________                                         SiO.sub.2                                                                              >58%             (for MgO =< 10%) and                                  SiO.sub.2                                                                              >58% + 0.5 (% MgO -10)                                                                          (for MgO >= 10%)                                      ______________________________________                                    

The applicants have further found that the Al₂ O₃ content is important. From their studies it appears that the maximum Al₂ O₃ content lies somewhere between 2.57% and 3.97%. The applicants have found that with increasing alumina levels the first material to crystallise is calcium aluminate and this possibly forms a liquid phase that assists flow and hence shrinkage.

Table 10 shows, for the same compositions as Table 9, 24 hour solubilities for each major constituent. It can be seen that all of the compositions have high solubilities.

As mentioned above use of CaO in forming calcium containing fibres is inconvenient and can be hazardous. The applicants investigated use of mixed oxide materials that would avoid the handling of CaO. A fibre was made by admixture of magnesia with silica and wollastonite (CaSiO₃).

The raw materials used to make the melt comprised:

Pennine Darlington Heavy Magnesia (#200)

    ______________________________________                                                MgO   92.60%                                                                   CaO   1.75%                                                                    Fe.sub.2 O.sub.3                                                                     0.04%                                                                    SiO.sub.2                                                                            0.20%                                                                    Cl    0.25%                                                                    SO.sub.3                                                                             0.70%                                                                    LOI   4.50%                                                             ______________________________________                                    

Partek's Finnish Low Iron Wollastonite (#200) (U.K. agent--Cornelius Chemical Co., Romford, Essex)

    ______________________________________                                                SiO.sub.2                                                                            51.80%                                                                   CaO   44.50%                                                                   MgO   0.80%                                                                    Al.sub.2 O.sub.3                                                                     0.60%                                                                    Fe.sub.2 O.sub.3                                                                     0.30%                                                                    Na.sub.2 O                                                                           0.10%                                                                    K.sub.2 O                                                                            0.05%                                                                    TiO.sub.2                                                                            0.05%                                                                    S     0.02%                                                                    MnO   0.01%                                                                    P     0.01%                                                                    F     0.01%                                                                    LOI   1.70%                                                             ______________________________________                                    

Hepworth Mineral's Redhill T washed silica sand

    ______________________________________                                                SiO.sub.2                                                                           99.0% min.                                                         ______________________________________                                    

These constituents were mixed as 78.65% Wollastonite; 19.25% SiO₂ ; and 3.6% MgO. This gave 0.4-0.5% of the final melt as Al₂ O₃.

It was surprisingly found that in producing a melt using these constituents the current requirements were only two-thirds that for the use of the raw oxides.

Fibre was produced by blowing (although spinning and other methods can be used). 2 runs were performed with different blowing conditions.

Chemical analysis was undertaken by the Analytical Department at the applicant's subsidiary Morgan Materials Technology (hereinafter called M² T) using wet chemical techniques. Fibre diameters were measured using M² T's Galai particle analyser, with shape analysis software. Typically 40,000 fibres were analysed for each run.

The first result of note was the speed of melt reaction when using wollastonite as compared with lime. Also the current was seen to be very stable throughout the growth of the melt. If the current was lost whilst pulling the electrodes apart the current could be restored simply by pushing them back together again. This was not possible with the runs using lime.

Chemical Analysis

    ______________________________________                                         Others   CaO    MgO    Al.sub.2 O.sub.3                                                                     SiO.sub.2                                                                           ZrO.sub.2                                                                            Na.sub.2 O                                                                          Total                             ______________________________________                                         Run1 0.7     32.6   3.8  0.8   60.1 0.8   0.5  99.3                            Run2 0.7     32.5   3.8  0.8   60.1 0.8   0.6  99.3                            ______________________________________                                    

Runs 1 and 2 indicate the respective x-ray fluorescence analyses for each run.

Shrinkage Results (1000° C. for 24 hours)

    ______________________________________                                                 L1  L2       L3    L4    Av.  Std. Dev.                                ______________________________________                                         Run 1     0.9   0.2      0.4 0.6   0.5  0.3                                    Run 2 (A) 1.0   -0.2     0.7 0.6   0.5  0.5                                    Run 2 (B) 0.5   0.2      0.0 0.4   0.2  0.2                                    ______________________________________                                    

Solubility Results (ppm)

    ______________________________________                                                   CaO        MgO    SiO.sub.2                                          ______________________________________                                         Run 1 (5 hr)                                                                               67           10      95                                            Run 1 (24 hr)                                                                              84           17     146                                            Run 2 (5 hr)                                                                               39            7      72                                            Run 2 (24 hr)                                                                              73           17     186                                            ______________________________________                                    

Fibre diameters

    ______________________________________                                         Mean        Median   100%<    % >5 μm                                                                            % <1 μm                                ______________________________________                                         Run 1  5.1 μm                                                                               3.4 μm                                                                               30 μm                                                                              33%    13%                                     Run 2  4.1 μm                                                                               2.7 μm                                                                               25 μm                                                                              25%    19%                                     ______________________________________                                    

Accordingly it appears to be the case that by using what are cheaper ingredients than the pure oxides one can obtain a fibre that has as high a performance as using purer oxides and at much improved energy costs and safety. It is to be noted that this feature of the invention is not limited to saline soluble fibres and any oxide fibre that contains both calcium and silicon can advantageously be made with a calcium silicate, wollastonite being merely an example of such a silicate.

The previous description is directed towards high temperature usage of particular saline soluble fibres. The following is directed towards the prediction and use of saline soluble fibres. A series of fritted glass melts were made of the compositions shown in Tables 11A and 11B and quenched in water. Solubilities of the various components of the quenched melt were measured by the previously described method of atomic absorption. The solubilities were normalised to a specific surface area of 0.25 m² /gram of fibre.

The free energy of hydration was calculated by normalising the chemical analysis to 100 weight %; making the assumption that simple silicates (MSiO₃ /M₂ SiO₃) are present and calculating the free energy of hydration contribution of each species; and summing to get the total free energy of hydration. The data in Tables 11A & 11B is also presented in FIG. 4. It can be seen that the fibres lie on a generally straight line bar four groups of materials that will be explained below.

Table 11 shows in each column the following:

Fibre Reference

Composition

Molar ratios

Moles/100 grams of melt

Species assumed (see below)

Calculated free energy of hydration of assumed species (kcal/100 grams)(see below)

Calculated free energy of hydration of assumed species (kJ/kg) (see below)

Solubility data (# indicates not measured [see below])

Specific surface area

Normalised solubility data

log normalised solubility

The base data on which calculation of the free energy of hydration was done is set out in Tables 12 which indicates free energies of hydration taken from the literature in the units kcal/mol and kJ/mol.

                                      TABLE 11                                     __________________________________________________________________________     Table of Free Energy of Hydration Values for Silicate Melts                    __________________________________________________________________________             Composition             Moles     Moles                                Melt Code                                                                              Oxide Wt. % Rationalized                                                                          Moles                                                                               in 100 g                                                                            Species                                                                             in 1 kg                              __________________________________________________________________________     CAS10(B) - A                                                                           CaO   47.2  47.8   0.852                                                                               0.451                                                                               CaSiO3                                                                              4.51                                         Al2O3 24.5  24.8   0.243                                                                               0.243                                                                               Al2O3                                                                               2.43                                         SiO2  27.1  27.4   0.451                                                                               0.401                                                                               CaO  4.01                                         Total 98.8  100.0                                                      CAS10(B) - B                                                                           CaO   46.5  47.2   0.842                                                                               0.479                                                                               CaSiO3                                                                              4.79                                         Al2O3 23.7  24.0   0.235                                                                               0.235                                                                               Al2O3                                                                               2.35                                         SiO2  28.4  28.8   0.479                                                                               0.363                                                                               CaO  3.63                                         Total 98.6  100.0                                                      CAS10(B) - C                                                                           CaO   47.8  48.4   0.863                                                                               0.456                                                                               CaSiO3                                                                              4.56                                         Al2O3 23.9  24.2   0.237                                                                               0.237                                                                               Al2O3                                                                               2.37                                         SiO2  27.1  27.4   0.456                                                                               0.407                                                                               CaO  4.07                                         Total 98.8  100.0                                                      CIS(A)  CaO   42.7  44.3   0.790                                                                               0.707                                                                               CaSiO3                                                                              7.07                                         TiO2  12.7  13.2   0.165                                                                               0.083                                                                               CaO  0.83                                         SiO2  41.0  42.5   0.707                                                                               0.165                                                                               TiO2 1.65                                         Total 96.4  100.0                                                      SrSiO3  SrO   63.1  64.4   0.622                                                                               0.592                                                                               SrSiO3                                                                              5.92                                         SiO2  34.9  35.6   0.592                                                                               0.030                                                                               SrO  0.30                                         Total 98.0  100.0                                                      CaSiO3  CaO   46.1  46.9   0.836                                                                               0.836                                                                               CaSiO3                                                                              8.36                                         SiO2  52.3  53.1   0.884                                                                               0.048                                                                               SiO2 0.48                                         Total 98.4  100.0                                                      NAS(A)  Na2O  18.8  18.9   0.305                                                                               0.305                                                                               Na2SiO3                                                                             3.05                                         Al2O3 39.7  39.8   0.390                                                                               0.390                                                                               Al2O3                                                                               3.90                                         SiO2  41.1  41.3   0.687                                                                               0.382                                                                               SiO2 3.82                                         Total 99.6  100.0                                                      CAS4    CaO   21.0  20.9   0.373                                                                               0.373                                                                               CaSiO3                                                                              3.73                                         Al2O3 35.4  35.2   0.345                                                                               0.345                                                                               Al2O3                                                                               3.45                                         SiO2  44.2  43.9   0.731                                                                               0.358                                                                               SiO2 7.31                                         Total 100.6 100.0                                                      MAS(B)  MgO   10.0  10.3   0.256                                                                               0.256                                                                               MgSiO3                                                                              2.56                                         Al2O3 33.7  34.9   0.342                                                                               0.342                                                                               Al2O3                                                                               3.42                                         SiO2  53.0  54.8   0.912                                                                               0.656                                                                               SiO2 6.56                                         Total 96.7  100.0                                                      SAS(A)  SrO   29.8  30.5   0.294                                                                               0.294                                                                               SrSiO3                                                                              2.94                                         Al2O3 31.1  31.8   0.312                                                                               0.312                                                                               Al2O3                                                                               3.12                                         SiO2  36.8  37.7   0.627                                                                               0.333                                                                               SiO2 3.33                                         Total 97.7  100.0                                                      SCS(A)  SrO   35.0  35.1   0.339                                                                               0.339                                                                               SrSiO3                                                                              3.39                                         CoO   21.0  21.1   0.376                                                                               0.376                                                                               CaSiO3                                                                              3.76                                         SiO2  43.6  43.8   0.729                                                                               0.014                                                                               SiO2 0.14                                         Total 99.6  100.0                                                      SMAS(A) SrO   55.0  56.6   0.546                                                                               0.296                                                                               SrSiO3                                                                              2.96                                         MgO   1.2   1.2    0.030                                                                               0.030                                                                               MgO  0.30                                         Al2O3 23.7  24.4   0.239                                                                               0.239                                                                               Al2O3                                                                               2.39                                         SiO2  17.3  17.8   0.296                                                                               0.250                                                                               SrO  2.50                                         Total 97.2  100.0                                                      SMAS(B) SrO   55.0  55.9   0.539                                                                               0.401                                                                               SrSiO3                                                                              4.01                                         MgO   4.8   4.9    0.122                                                                               0.122                                                                               MgO  1.22                                         Al2O3 14.8  15.1   0.148                                                                               0.148                                                                               Al2O3                                                                               1.48                                         SiO2  23.7  24.1   0.401                                                                               0.138                                                                               SrO  1.38                                         Total 98.3  100.0                                                      SMS(A)  SrO   33.0  32.9   0.318                                                                               0.318                                                                               SrSiO3                                                                              3.18                                         MgO   12.5  12.5   0.310                                                                               0.310                                                                               MgSiO3                                                                              3.10                                         Al2O3 1.0   1.0    0.010                                                                               0.010                                                                               Al2O3                                                                               0.10                                         SiO2  53.8  53.6   0.892                                                                               0.264                                                                               SiO2 2.64                                         Total 100.3 100.0                                                      SAS(C)  SrO   56.0  56.2   0.542                                                                               0.401                                                                               SrSiO3                                                                              4.01                                         Al2O3 19.7  19.7   0.193                                                                               0.193                                                                               Al2O3                                                                               1.93                                         SiO2  24.0  24.1   0.401                                                                               0.141                                                                               SrO  1.41                                         Total 99.7  100.0                                                      CMAS(A) CaO   35.0  34.6   0.617                                                                               0.293                                                                               CaSiO3                                                                              2.93                                         MgO   4.5   4.4    0.109                                                                               0.109                                                                               MgO  1.09                                         Al2O3 44.0  43.4   0.426                                                                               0.426                                                                               Al2O3                                                                               4.26                                         SiO2  17.8  17.6   0.293                                                                               0.324                                                                               CaO  3.24                                         Total 101.3 100.0                                                      SWA2    CaO   21.7  21.7   0.387                                                                               0.387                                                                               CaSiO3                                                                              3.87                                         MgO   15.7  15.7   0.389                                                                               0.389                                                                               MgSiO3                                                                              3.89                                         Al2O3 0.8   0.8    0.008                                                                               0.008                                                                               Al2O3                                                                               0.08                                         SiO2  61.8  61.8   1.028                                                                               0.252                                                                               SiO2 2.52                                         Total 100.0 100.0                                                      SAS(D)  SrO   56.5  57.3   0.553                                                                               0.413                                                                               SrSiO3                                                                              4.13                                         Al2O3 17.6  17.9   0.176                                                                               0.176                                                                               Al2O3                                                                               1.76                                         SiO2  24.4  24.8   0.413                                                                               0.140                                                                               SrO  1.40                                         Total 98.5  100.0                                                      KHAS(A) K2O   16.5  16.5   0.175                                                                               0.175                                                                               K2SiO3                                                                              1.75                                         MgO   13.0  13.0   0.323                                                                               0.323                                                                               MgSiO3                                                                              3.23                                         Al2O3 18.0  17.9   0.176                                                                               0.176                                                                               Al2O3                                                                               1.76                                         SiO2  52.8  52.6   0.875                                                                               0.377                                                                               SiO2 8.75                                         Total 100.3 100.0                                                      __________________________________________________________________________            Free Energy of                                                                           Free Energy of                                                                         Solubility                                                                             S.S.A                                                                             Normalized                                                                           Log (norm                            Melt Code                                                                             Hydration (kcal/100 g)                                                                   Hydration (kJ/kg)                                                                      Oxide                                                                              (ppm)                                                                              m2/g                                                                              Solubility                                                                           solub)                               __________________________________________________________________________     CAS10(B) - A                                                                          -7.3      -304.0  CaO  44 0.30                                                                              43    1.63                                        0.8       31.6    Al2O3                                                                               0                                                       -5.3      -219.7  SiO2                                                                                7                                                       -11.8     -492.1  Total                                                                               51                                               CAS10(B) - B                                                                          -7.7      -322.8  CaO  58 0.39                                                                              66    1.82                                        0.7       30.6    Al2O3                                                                               1                                                       -4.8      -198.9  SiO2                                                                                44                                                      -11.8     -491.1  Total                                                                              103                                               CAS10(B) - C                                                                          -7.3      -307.3  CaO  55 0.36                                                                              76    1.88                                        0.7       30.8    Al2O3                                                                               0                                                       -5.3      -223.0  SiO2                                                                                55                                                      -11.9     -499.5  Total                                                                              110                                               CIS(A) -11.4     -476.5  CaO  62 0.40                                                                              69    1.84                                        -1.1      -45.5   TiO2                                                                                0                                                       2.6       110.4   SiO2                                                                                49                                                      -9.9      -411.6  Total                                                                              111                                               SrSiO3 -14.4     -604.4  SrO  2  0.37                                                                              249   2.40                                        -0.5      -21.7   SiO2                                                                               367                                                      -14.9     -626.1  Total                                                                              369                                               CaSiO3 -13.5     -563.5  CaO  41 0.45                                                                              163   2.21                                        0.3       11.2    SiO2                                                                               253                                                      -13.2     -552.3  Total                                                                              294                                               NAS(A) -8.8      -367.5  Na2O                                                                               #   0.56                                                                              4     0.60                                        1.2       50.7    Al2O3                                                                               4                                                       2.1       89.7    SiO2                                                                                5                                                       -5.5      -227.4  Total                                                                               9                                                CAS4   -6.0      -251.4  CaO  11 0.62                                                                              8     0.90                                        1.1       44.9    Al2O3                                                                               4                                                       2.0       171.1   SiO2                                                                                5                                                       -2.9      -35.4   Total                                                                               20                                               MAS(B) -3.6      -149.0  MgO  7  0.52                                                                              6     0.78                                        1.1       44.5    Al2O3                                                                               2                                                       3.7       153.5   SiO2                                                                                4                                                       1.2       49.0    Total                                                                               13                                               SAS(A) -7.2      -300.2  SrO  9  0.50                                                                              8     0.90                                        1.0       40.6    Al2O3                                                                               2                                                       1.9       77.9    SiO2                                                                                5                                                       -4.3      -181.7  Total                                                                               16                                               SCS(A) -8.3      -346.1  SrO  75 0.41                                                                              280   2.45                                        -6.1      -253.4  CaO  30                                                      0.1       3.3     SiO2                                                                               355                                                      -14.3     -596.2  Total                                                                              460                                               SMAS(A)                                                                               -7.2      -302.2  SrO  57 0.46                                                                              38    1.58                                        -0.2      -8.2    MgO  2                                                       0.7       31.1    Al2O3                                                                               5                                                       -4.3      -181.0  SiO2                                                                                5                                                       -11.0     -460.3  Total                                                                               69                                               SMAS(B)                                                                               -9.8      -409.4  SrO 110 0.39                                                                              95    1.98                                        -0.8      -33.2   MgO  15                                                      0.5       19.2    Al2O3                                                                               1                                                       -2.4      -99.9   SiO2                                                                                22                                                      -12.5     -523.3  Total                                                                              148                                               SMS(A) -7.8      -324.7  SrO 147 0.39                                                                              212   2.33                                        -4.3      -180.4  MgO  61                                                      0.0       1.3     Al2O3                                                                               0                                                       1.5       61.8    SiO2                                                                               123                                                      -10.6     -442.0  Total                                                                              331                                               SAS(C) -9.8      -409.4  SrO  70 0.38                                                                              52    1.72                                        0.6       25.1    Al2O3                                                                               1                                                       -2.4      -102.1  SiO2                                                                                8                                                       -11.6     -486.4  Total                                                                               79                                               CMAS(A)                                                                               -4.7      -197.5  CaO  11 0.30                                                                              24    1.38                                        -0.7      -29.6   MgO  7                                                       1.3       55.4    Al2O3                                                                               3                                                       -4.2      -177.6  SiO2                                                                                8                                                       -8.3      -349.3  Total                                                                               29                                               SWA2   -6.2      -260.8  CaO  53 0.48                                                                              119   2.08                                        -5.4      -226.4  MgO  57                                                      0.0       1.0     Al2O3                                                                               0                                                       1.4       59.0    SiO2                                                                               118                                                      -10.2     -427.2  Total                                                                              228                                               SAS(D) -10.1     -421.7  SrO 107 0.40                                                                              92    1.96                                        0.5       22.9    Al2O3                                                                               1                                                       -2.4      -101.4  SiO2                                                                                39                                                      -12.0     -500.2  Total                                                                              147                                               KHAS(A)                                                                               -7.3      -305.4  K2O #   0.36                                                                              14    1.15                                        -2.1      -188.0  MgO  8                                                       0.5       22.9    Al2O3                                                                               1                                                       2.1       204.8   SiO2                                                                                11                                                      -6.8      -265.7  Total                                                                               20                                               __________________________________________________________________________

                  TABLE 12                                                         ______________________________________                                                              G.sub.hyd                                                                      (kcal/mole)                                                                            (kJ/mol)                                          ______________________________________                                         Relevant oxides                                                                SiO.sub.2 + H.sub.2 O → H.sub.2 SiO.sub.3                                                      5.6       23.4                                          (vitreous silica)                                                              Al.sub.2 O.sub.3 + 3H.sub.2 O → 2A1(OH).sub.3                                                  3.1       13.0                                          MgO + H.sub.2 O → Mg(OH).sub.2                                                                 -6.5      -27.2                                         CaO + H.sub.2 O → Ca(OH).sub.2                                                                 -13.1     -54.8                                         SrO + H.sub.2 O → Sr(OH).sub.2                                                                 -17.3     -72.4                                         Na.sub.2 O + H.sub.2 O → 2NaOH                                                                 -33.5     -140.2                                        K.sub.2 O + H.sub.2 O → 2KOH                                                                   -46.1     -192.9                                        TiO.sub.2 + H.sub.2 O → Ti(OH).sub.2 O                                                         16.0      66.9                                          P.sub.2 O.sub.5 + 3H.sub.2 O → 2H.sub.3 PO.sub.4                                               -55.9     -233.9                                        B.sub.2 O.sub.3 + 3H.sub.2 O → 2H.sub.3 BO.sub.3                                               -9.8      -41.0                                         ZrO.sub.2 + H.sub.2 O → Zr(OH).sub.2 O                                                         -7.1      -29.7                                         Relevant Silicates                                                             Na.sub.2 SiO.sub.3 + 2H.sup.+  (aq) → H.sub.2 SiO.sub.3                 + 2Na.sup.+  (aq)      -28.8     -120.5                                        K.sub.2 SiO.sub.3 + 2H.sup.+  (aq) → H.sub.2 SiO.sub.3 + 2K.sup.+       (aq)                   -41.7     -174.5                                        MgSiO.sub.3 + 2H.sup.+ -13.9 → H.sub.2 SiO.sub.3 + Mg.sup.2+                                             -58.2                                         CaSiO.sub.3 + 2H.sup.+ -16.1 → H.sub.2 SiO.sub.3 + Ca.sup.2+                                             -67.4                                         SrSiO.sub.3 + 2H.sup.+ -24.4 → H.sub.2 SiO.sub.3 + Sr.sup.2+                                             -102.1                                        BaSiO.sub.3 + 2H.sup.+ -37.3 → H.sub.2 SiO.sub.3 + Ba.sup.2+                                             -156.1                                        ZnSiO.sub.3 + 2H.sup.+ -2.4) → H.sub.2 SiO.sub.3 + Zn.sup.2+                                             -10.0                                         Disilicates                                                                    Ca.sub.2 SiO.sub.4 + 3H.sup.+  (aq) → H.sub.2 SiO.sub.3                 + 2Ca.sup.2+  + OH.sup.-                                                                              -30.3     -126.8                                        Sr.sub.2 SiO.sub.4 + 3H.sup.+  (aq) → H.sub.2 SiO.sub.3                 + 2Sr.sup.2+  + OH.sup.-                                                                              -50.3     -210.5                                        Mg.sub.2 SiO.sub.4 + 3H.sup.+  (aq) → H.sub.2 SiO.sub.3                 + 2Mg.sup.2+  + OH.sup.-                                                                              -17.9     -74.9                                         ______________________________________                                    

Although calculations were undertaken assuming the presence of the simplest silicates choice of other silicates (such as disilicates) does not appear to change the calculations much. For example given below is the calculation for an assumed composition which shows only minor differences for the free energy of hydration calculated.

    ______________________________________                                         Composition (moles/100 g)                                                                       0.767 CaO                                                                      0.417 MgO                                                                      0.669 SiO.sub.2                                               0.384 Ca.sub.2 SiO.sub.4 =                                                               -11.6      or     0.433 CaSiO.sub.3 =                                                                      -7.0                                     0.285 MgSiO.sub.3 =                                                                      -4.0              0.236 MgSiO.sub.3 =                                                                      -3.3                                     0.132 MgSiO.sub.3 =                                                                      -0.9              0.334 CaO =                                                                              -4.4                                               -16.5             0.181 MgO =                                                                              -1.2                                                                           -15.9                                                         or     0.384 Ca.sub.2 SiO.sub.4 =                                                               -11.6                                                                0.132 Mg.sub.2 SiO.sub.4 =                                                               -2.4                                                                 0.153 MgSiO.sub.3 =                                                                      -2.1                                                                           -16.1                                    ______________________________________                                    

The applicants have found that when the free energy of hydration is more negative than -10 kcal/100 grams (-418.4 kJ/kg) of composition the composition showed high solubility. The compositions where this relationship broke down were those for which the total solubility was not available (for example those materials containing sodium, where any dissolved sodium would be swamped by the sodium in the saline solution) or where the free energy of hydration of the most likely species present was not available from the literature.

As a test of this technique the two examples of European Patent No. 0399320 were examined. The disclosed examples had the compositions:

    ______________________________________                                                      Composition 1                                                                             Composition 2                                          Component    Weight percent                                                                            Weight percent                                         ______________________________________                                         SiO.sub.2    60.7       58.5                                                   Al.sub.2 O.sub.3                                                                            --         5.8                                                    CaO          16.5       3.0                                                    MgO          3.2        --                                                     B.sub.2 O.sub.3                                                                             3.3        11.0                                                   Na.sub.2 O   15.4       9.8                                                    K.sub.2 O    0.7        2.9                                                    Iron oxide   0.2        0.1                                                    BaO          --         5.0                                                    ZnO          --         3.9                                                    ______________________________________                                    

Using the above method of calculation Composition 1 had a free energy of hydration of -11.6 kcal/100 grams (-485.3 kJ/kg) whereas Composition 2 had a free energy of hydration of -5.8 kcal/100 grams (-242.6 kJ/kg). This would suggest that Composition 1 would be a saline soluble fibre, and hence physiologically safer than an insoluble fibre; whereas Composition 2 would be predicted to be a relatively insoluble fibre and hence less safe. This is what is disclosed in EP 0399320, the fibres of Composition 2 having a longer lifetime in studies in which the fibres were introduced interperitoneally into rats.

As mentioned above this predictive test can fail under some circumstances. To avoid these difficulties the applicants looked to a different predictive technique, namely the assessment of the amount of non-bridging oxygens present. This is calculated by normalising the chemical analysis to 100 weight %; calculating the molar percentage of each oxide; summing the oxygen-weighted contribution of each oxide to get the total number of oxygens; summing the weighted contribution of each oxide of non-bridging oxygens (see below); and taking the ratio of non-bridging oxygens to the total number of oxygens. The applicants have found that when this figure exceeds 30% the fibres are soluble.

To explain the term non-bridging oxygen one must look to the structure of glasses. Glasses are very stiff liquids and to form usually require the presence of a material that can form a network (usually an oxygen-bridged network). The network may be modified by constituents that contribute non-bridging parts to the network and open the structure of the network and so prevent crystallisation. These materials are usually referred to as network-formers and modifiers respectively.

The terms modifier and network former are well known in the glass industries. Network formers are materials such as SiO₂, P₂ O₅, B₂ O₃ and GeO₂ which can form an interconnected network to form the glassy phase. Modifiers are substances such as CaO, Na₂ O, and K₂ O which alter the network and have effects on such properties as viscosity and melting point. There are some intermediate materials (such as Al₂ O₃, TiO₂, PbO, ZnO and BeO) which can act as both network formers and modifiers depending on the environment and on the amount present.

In the above mentioned test, for calculating the non-bridging oxygens, one ignores the network formers and calculates the contribution of each other oxide. The contribution of each oxide depends on the geometry and charge of each cation in the glass. As examples typical contributions are as follows:

Ca²⁺, Mg²⁺, Sr²⁺ and other divalent network modifier cations contribute 2 non-bridging oxygens

K⁺, Na⁺ and other monovalent network modifier cations contribute 1 non-bridging oxygen

Al³⁺, Ti³⁺ and other intermediate cations contribute -1 non-bridging oxygen (i.e these oxides reduce the number of non-bridging oxygens)

(Ti⁴⁺ is reduced to Ti³⁺ in most glasses when present in relatively small quantities)

                                      TABLE 13                                     __________________________________________________________________________            Composition     Oxygen         Solubility                                                                               S.S.A                                                                              Normalized                                                                           Log (norm            Melt Code                                                                             Oxide                                                                              Wt. %                                                                              Moles                                                                              Mol. %                                                                             Total                                                                               N.B.O.                                                                              % N.B.O                                                                             Oxide                                                                               (ppm)                                                                               m2/g                                                                               Solubility                                                                           solub)               __________________________________________________________________________     CAS10(B) - A                                                                          CaO 47.2                                                                               0.842                                                                              54.9                                                                               160.8                                                                               78.4 48.8 CaO   44  0.30                                                                               43    1.63                        Al2O3                                                                              24.5                                                                               0.240                                                                              15.7               Al2O3                                                                                0                                         SiO2                                                                               27.1                                                                               0.451                                                                              29.4               SiO2  7                                             Total                                                                              1.533                                                                              100.0              Total                                                                                51                                 CAS10(B) - B                                                                          CaO 46.5                                                                               0.829                                                                              54.0                                                                               160.9                                                                               77.8 48.4 CaO   58  0.39                                                                               66    1.82                        Al2O3                                                                              23.7                                                                               0.232                                                                              15.1               Al2O3                                                                                1                                         SiO2                                                                               28.4                                                                               0.473                                                                              30.8               SiO2  44                                            Total                                                                              1.534                                                                              100.0              Total                                                                               103                                 CAS10(B) - C                                                                          CaO 47.8                                                                               0.852                                                                              55.4                                                                               159.6                                                                               80.4 50.4 CaO   55  0.36                                                                               76    1.88                        Al2O3                                                                              23.9                                                                               0.234                                                                              15.2               Al2O3                                                                                0                                         SiO2                                                                               27.1                                                                               0.451                                                                              29.3               SiO2  55                                            Total                                                                              1.537                                                                              100.0              Total                                                                               110                                 CTS(A) CaO 42.7                                                                               0.761                                                                              47.5                                                                               152.5                                                                               85.1 55.8 CaO   62  0.40                                                                               69    1.84                        TiO2                                                                               12.7                                                                               0.159                                                                              9.9                TiO2  0                                         SiO2                                                                               41.0                                                                               0.682                                                                              42.6               SiO2  49                                            Total                                                                              1.602                                                                              100.0              Total                                                                               111                                 SrSiO3 SrO 63.1                                                                               0.609                                                                              51.2                                                                               148.8                                                                               102.4                                                                               68.8 SrO   2   0.37                                                                               249   2.40                        SiO2                                                                               34.9                                                                               0.581                                                                              48.8               SiO2 367                                            Total                                                                              1.190                                                                              100.0              Total                                                                               369                                 CaSiO3 CaO 46.1                                                                               0.822                                                                              48.6                                                                               151.4                                                                               97.2 64.2 CaO   41  0.45                                                                               163   2.21                        SiO2                                                                               52.3                                                                               0.870                                                                              51.4               SiO2 253                                            Total                                                                              1.692                                                                              100.0              Total                                                                               294                                 NAS(A) Na2O                                                                               18.8                                                                               0.303                                                                              22.0                                                                               228.3                                                                               -12.6                                                                               -5.5 Na2O #    0.56                                                                               4     0.60                        Al2O3                                                                              39.7                                                                               0.389                                                                              28.3               Al2O3                                                                                4                                         SiO2                                                                               41.1                                                                               0.684                                                                              49.7               SiO2  5                                             Total                                                                              1.376                                                                              100.0              Total                                                                                9                                  CAS4   CaO 21.0                                                                               0.374                                                                              25.7                                                                               198.1                                                                               3.8  1.9  CaO   11  0.62                                                                               8     0.90                        Al2O3                                                                              35.4                                                                               0.347                                                                              23.8               Al2O3                                                                                4                                         SiO2                                                                               44.2                                                                               0.736                                                                              50.5               SiO2  5                                             Total                                                                              1.457                                                                              100.0              Total                                                                                20                                 MAS(B) NgO 10.0                                                                               0.248                                                                              17.0                                                                               205.6                                                                               -11.2                                                                               -5.4 MgO   7   0.52                                                                               6     0.78                        Al2O3                                                                              33.7                                                                               0.311                                                                              22.6               Al2O3                                                                                2                                         SiO2                                                                               53.0                                                                               0.882                                                                              60.4               SiO2  4                                             Total                                                                              1.461                                                                              100.0              Total                                                                                13                                 SAS(A) SrO 29.8                                                                               0.288                                                                              23.9                                                                               201.4                                                                               -2.6 -1.4 SrO   9   0.50                                                                               8     0.90                        Al2O3                                                                              31.1                                                                               0.305                                                                              25.3               Al2O3                                                                                2                                         SiO2                                                                               36.8                                                                               0.612                                                                              50.8               SiO2  5                                             Total                                                                              1.205                                                                              100.0              Total                                                                                16                                 SCS(A) SrO 35.0                                                                               0.338                                                                              23.5                                                                               150.5                                                                               99.0 65.8 SrO   75  0.41                                                                               280   2.45                        CaO 21.0                                                                               0.374                                                                              26.0               CaO   30                                        SiO2                                                                               43.6                                                                               0.726                                                                              50.5               SiO2 355                                            Total                                                                              1.438                                                                              100.0              Total                                                                               460                                 SMAS(A)                                                                               SrO 55.0                                                                               0.531                                                                              49.1                                                                               169.6                                                                               60.8 35.8 SrO   57  0.46                                                                               38    1.58                        MgO 1.2 0.030                                                                              2.8                MgO   5                                         Al2O3                                                                              23.7                                                                               0.232                                                                              21.5               Al2O3                                                                                2                                         SiO2                                                                               17.3                                                                               0.288                                                                              26.6               SiO2  5                                             Total                                                                              1.081                                                                              100.0              Total                                                                                69                                 SMAS(B)                                                                               SrO 55.0                                                                               0.531                                                                              44.6                                                                               157.6                                                                               84.8 53.8 SrO  110  0.39                                                                               95    1.98                        MgO 4.8 0.119                                                                              10.0               MgO   15                                        Al2O3                                                                              14.8                                                                               0.145                                                                              12.2               Al2O3                                                                                1                                         SiO2                                                                               23.7                                                                               0.394                                                                              33.2               SiO2  22                                            Total                                                                              1.189                                                                              100.0              Total                                                                               148                                 SMS(A) SrO 33.0                                                                               0.318                                                                              20.7                                                                               159.5                                                                               80.6 50.5 SrO  147  0.39                                                                               212   2.33                        MgO 12.5                                                                               0.310                                                                              20.2               MgO   61                                        Al2O3                                                                              1.0 0.010                                                                              0.6                Al2O3                                                                                0                                         SiO2                                                                               53.8                                                                               0.895                                                                              58.4               SiO2 123                                            Total                                                                              1.533                                                                              100.0              Total                                                                               331                                 SAS(C) SrO 56.0                                                                               0.540                                                                              47.7                                                                               169.3                                                                               61.4 36.3 SrO   70  0.38                                                                               52    1.72                        Al2O3                                                                              19.7                                                                               0.193                                                                              17.0               Al2O3                                                                                1                                         SiO2                                                                               24.0                                                                               0.399                                                                              35.3               SiO2  8                                             Total                                                                              1.132                                                                              100.0              Total                                                                                79                                 CMAS(A)                                                                               CaO 35.0                                                                               0.624                                                                              42.6                                                                               179.3                                                                               41.4 23.1 CaO   11  0.30                                                                               24    1.38                        MgO 4.5 0.112                                                                              7.6                MgO   7                                         Al2O3                                                                              44.0                                                                               0.432                                                                              29.5               Al2O3                                                                                3                                         SiO2                                                                               17.8                                                                               0.296                                                                              20.3               SiO2  8                                             Total                                                                              1.464                                                                              100.0              Total                                                                                29                                 SWA2   CaO 21.1                                                                               0.387                                                                              21.4                                                                               157.5                                                                               85.0 54.0 CaO   53  0.48                                                                               119   2.08                        MgO 15.7                                                                               0.389                                                                              21.5               MgO   57                                        Al2O3                                                                              0.8 0.008                                                                              0.4                Al2O3                                                                                0                                         SiO2                                                                               61.8                                                                               1.028                                                                              56.7               SiO2 118                                            Total                                                                              1.812                                                                              100.0              Total                                                                               228                                 SAS(D) SrO 56.5                                                                               0.545                                                                              48.5                                                                               166.9                                                                               66.2 39.7 SrO  107  0.40                                                                               92    1.96                        Al2O3                                                                              17.6                                                                               0.173                                                                              15.4               Al2O3                                                                                1                                         SiO2                                                                               24.4                                                                               0.406                                                                              36.1               SiO2  39                                            Total                                                                              1.124                                                                              100.0              Total                                                                               147                                 KMAS(A)                                                                               K2O 16.5                                                                               0.175                                                                              11.3                                                                               179.5                                                                               41.4 23.1 K2O  #    0.36                                                                               14    1.15                        MgO 13.0                                                                               0.323                                                                              20.8               MgO   8                                         Al2O3                                                                              18.0                                                                               0.177                                                                              11.4               Al2O3                                                                                1                                         SiO2                                                                               52.8                                                                               0.879                                                                              56.6               SiO2  11                                            Total                                                                              1.554                                                                              100.0              Total                                                                                20                                 __________________________________________________________________________

Table 13 shows, for the compositions of Table 11, the calculated figure for non-bonding oxygens and these figures are reproduced in FIG. 5. It can be seen that the plot of FIG. 5 is more linear than that of FIG. 4. Compositions with greater than 30% non-bridging oxygens show high solubility.

To illustrate the method the calculation for one example (the first shown in Table 13) is given below:

    ______________________________________                                         Mols/     Total         Non-bridging                                           Mol       Oxygen        Oxygens                                                ______________________________________                                         CaO   0.549   0.549             1.098                                                                               (2*0.549)                                 Al.sub.2 O.sub.3                                                                     0.157   0.471    (0.157*3)                                                                             -0.314 (-1*0.157*2A1)                            SiO.sub.2                                                                            0.294   0.588             0.000                                                1.000   1.608             0.784                                          ______________________________________                                          % nonbridging oxygens (0.784/1.608)*100 = 48.8%                          

As an example one can look to European Patent Specification No. 0399320 referred to above. Using this method in relation to that specification Composition 1 has a non-bridging oxygen percentage of 48.2% whereas Composition 2 has a non-bridging oxygen percentage of 19.6%, again predicting that Composition 1 is more soluble than Composition 2.

There is a further criterion which a composition must meet for it to form vitreous fibres, namely that it be capable of forming a glass. The applicants have found a simple test. If the ratio of modifiers to network formers is less than a critical value (for SiO₂ based glasses, 1) the composition will generally form a glass. For the purpose of this test reasonable results are obtained if such intermediate materials are treated as networkers. Table 14 shows for a series of compositions in each column:

Fibre reference (N.B. these are not the same fibres as shown in tables 9 & 10)

Composition

Molar ratios

Ratio of glass modifiers to network formers

Free energy of hydration of raw oxides

Melting Point

X-ray diffraction results

Solubility data (# indicates not measured)

Specific surface area

Normalised solubility data

Arbitrary ranking as to solubility and glass forming ability

Indication as to whether melting point above 1500° C.

It should be emphasised that this test is a screening one rather than a wholly predictive one as there are several circumstances that may lead to its failure. Among these circumstances are compound formation and inability to quench fast enough to form glass.

Having adopted these tests as a screening method there follows a further step to ascertain whether the composition will form a vitreous fibre. This last step is best examined experimentally as fibre forming ability is a complex function of many physical characteristics, e.g. viscosity, which are often difficult to measure.

    ______________________________________                                         Key to FIG. 1                                                                  ______________________________________                                         CR      Cristobalite    FO     Forsterite                                      TR      Tridymite       PR     Protoenstatite                                  PS      Pseudowollastonite                                                                             DI     Diopside                                        WO      Wollastonite    AK     Akermanite                                      RA      Rankinite       ME     Merwinite                                       LI      Lime            MO     Monticellite                                    PE      Periclase                                                              ______________________________________                                    

    TABLE 14        -         Norm Solub Criteria        Composition Molar Modifier/ Ghyd M. Pt.  Solubility Data (ppm) S.S.A.      (0.25 m2/g) (0-     10 Rating) M. Pt        Reference (Wt. %) Ratios Networker (kcal/mol) (C.) % RD Data Species 1        day Total 5 days Total (m2/g) 1 day 5 days Solub Glass >1500 C.        CAS10(A) 49.4 CaO  3.8 CaO 0.97  1544 Amorphous * trace CaO 62  48      0.25 124 187 10 9 T        No. 18 23.4 Al2O3  1.0 Al2O3  -4.6 (Eut.) (3 small peaks) Al2O3 7 124      10 182         29.2 SiO2       1.9 SiO2     SiO2 55  124                                   CIS(A) 42.7        CaO  4.7 CaO 0.85  1425 Amorphous CaO 100  88  0.56 83 88 7 10 W             No. 19 13.0 TiO2  1.0 TiO2  -1.3 (Eut.) (No peaks) TiO2 0 187 0      197         43.6 SiO2       4.5 SiO2     SiO2 87  109                                   MAS(A) 12.4        MgO  1.2 MgO 0.2  1450 Amorphous * trace MgO 63  248  0.57 40 116 4 9      W        No. 20 26.5 Al2O3  1.0 Al2O3  3.8 (1400 C.) (2 small peaks) Al2O3 5 92        1 264         62.4 SiO2       4.0 SiO2     SiO2 24  15                                    MAS(A) 29.4        Na2O  1.2 Na2O 0.69  1475 Crystalline Na2O #  #  0.53 15 471 1 2 W           No. 21 39.2 Al2O3  1.0 Al2O3  -6.3 (Eut.) (Glossy trace) Al2O3 3 37      9 83 990         33.7 SiO2       1.5 SiO2     SiO2 29  15                                    CPI(A) 53.3        CaO  2.7 CaO 1.35 -24.7 1565 Crystalline CaO 47 47 17 17 0.68 17 6 1 0        T        No. 22 50.6 P2O5       1.0 P2O5   (Eut.) (No glass) P2O5 #  #                SAI(B) 68.0 SiO      1.1 SiO 1.1 -5.7 1545 Amorphous (strong) * SiO 11 1247 5 729 0.88 346      203 10 5 T        No. 23 35.9 SiO2  1.0 SiO2   (Eut.) some crystal. (strong) SiO2 1236      724        CaSiO3 42.3 CaO  1.0 CaO 0.77 -3 1545 Amorphous * trace CaO 19 1284 27        508 0.71 452 179 10 9 T        No. 24 57.2 SiO2  1.3 SiO2   (1460 C.) (3 small peaks) SiO2 1265  481        ASI(D) 37.3 MgO  1.0 MgO 0.91 0.6 1545 Crystalline (strong) * MgO 62      216 249 362 0.83 65 127 5 6 T        No. 26 62.5 SiO2  1.1 SiO2   (Eut.) some glass (strong) SiO2 154  113        C612A17 47.7 CaO 11.2 CaO 0.8 -7.2 1400 Amorphous * trace CaO 14 317 3        145 2.45 37 15 3 7 W        No. 28 53.9 Al2O3  7.0 Al2O3   (Eut.) (Mod. cryst.) Al2O3 298  142           CMS(A) 42.5 CaO  1.8 CaO 7  1575 Crystalline CaO 42  21  0.47 158      118 10 0 T        No. 27 16.6 MgO  1.0 MgO  -4.3 (Eut.) (No glass) MgO 41 303 8 227             39.7 SiO2       1.4 SiO2     SiO2 220  198                              CTI(D) 15.4 CaO         1.0 CaO 4.570 9.5 1465 Crystalline CaO 14 14 16 16 1.15 3 3 0 0 W           No. 25 77.5 TiO2       3.5 TiO2   (Eut.) (No glass) TiO2 0  0             NCS(A) 20.4 Na2O      1.0 Na2O 1.86  1425 Crystalline * Na2O #  #  0.99 204 95 10 4 W        Cryst. 35.8 CaO  1.9 CaO  -8.7 (Eut.) some glass CaO 595 806 333 375         No. 29 40.8 SiO2       2.1 SiO2    (Strong cryst.) SiO2 211  42             NCS(A) 19.5 Na2O      1.0 Na2O 1.74  1425 Amorphous * Na2O #  #  1.36 123 49 10 7 W        Glassy 35.3 CaO  2.0 CaO  -8.1 (Eut.) some crystal. CaO 543 686 237      271        No. 30 42.7 SiO2       2.3 SiO2    (8 small peaks) SiO2 143  34              CPI(A)Rpt 54.4      CaO  2.9 CaO 1.45 -24 1565 Crystalline CaO 14 14 13 13 1.04 3 3 0 0 T          No. 31 48.2 P2O5       1.0 P2O5   (Eut.) (No glass) P2O5 #  #              NAS(A) 21.0 Na2O      1.0 Na2O 0.48  1475 Amorphous Na2O #  #  0.53 17 24 1 10 W        Apt. 40.1 Al2O3  1.2 Al2O3  -4 (Eut.) (No peaks) Al2O3 18 37 30 50           No. 32 38.7 SiO2       1.8 SiO2     SiO2 19  20                           KAS(E) 20.0 K2O  1.0        K2O 0.31  1590 Amorphous K2O #  #  0.97 7 10 1 10 T        No. 33 30.4 Al2O3  1.4 Al2O3  -2.7 (Eut.) (No peaks) Al2O3 9 28 18 39         46.1 SiO2       3.6 SiO2     SiO2 19  21                                    CAS4 21.2      CaO       1.1 CaO 0.26  1550 Amorphous CaO 17  13  0.72 10 8 1 10 T      No. 34 34.0 Al2O3  1.0 Al2O3  1.1 (1500 C.) (No peaks) Al2O3 1 28 1 24          44.6 SiO2       2.2 SiO2     SiO2 10  10                                   NAS(D) 14.9      MgO       2.7 MgO 0.24  1450 Amorphous MgO 7  68  0.61 6 42 1 10 W      No. 35 35.9 Al2O3  2.0 Al2O3  3.4 (1400 C.) (No peaks) Al2O3 1 15 24 107         51.6 SiO2       4.9 SiO2     SiO2 7  20                                     SAS(A) 32.5        SiO       1.0 SiO 0.25  1670 Amorphous SiO 24  1  0.67 19 4 2 10 T           No.      36 32.4 Al2O3       1.0 Al2O3  0.1 (7) (No peaks) Al2O3 11 50 1 12              38.1 SiO2      2.0 SiO2     SiO2 15  10        SCS(A) 17.1 SiO  1.1 SiO 0.91  1480 Amorphous * trace SiO 57  3  0.57      177 258 10 10 W        No. 37 17.5 CaO  1.0 CaO  -3.6 (Eut) (2 small peaks) CaO 35 411 2 599         43.4 SiO2       2.3 SiO2     SiO2 329  594                                  SCS(C) 19.5        SiO  0.5 SiO 0.9  1500 Amorphous SiO 55  11  0.66 155 219 10 10 T            No. 38 29.4 CaO  1.4 CaO  -3.1 (Eut.) (No peaks) CaO 36 411 10 579         47.1 SiO2       2.1 SiO2     SiO2 320  558                                  SCS(B) 51.4        SiO  1.7 SiO 0.96  1500 Amorphous * trace SiO 5  45  0.66 161 219 10      10 T        No. 39  8.1 CaO  0.5 CaO  -4.6 (Eut.) (1 small peak) CaO 5 425 27 579         39.7 SiO2       2.3 SiO2     SiO2 415  507                                  SAS(B) 65.9        SiO  5.2 SiO 0.96  1600 Crystalline (strong) * SiO 102  5  0.99 114 65        10 5 T        No. 40 12.4 Al2O3  1.0 Al2O3  -6.6 (7) some glass (strong) Al2O3 1 453        1 256         25.0 SiO2       3.4 SiO2     SiO2 350  250                                  SMAS(A)      58.0 SiO  2.7 SiO 0.76  1610 Amorphous * trace SiO 87  61  0.65 48 31 4      10 T        No. 41  1.1 MgO  0.1 MgO  -6.7 (1560 C.) (1 small peak) MgO 7 104 4 81         25.8 Al2O3       0.9 Al2O3     Al2O3 1  1                                    18.4 SiO2      1.1 SiO2     SiO2 9  15        SMAS(B) 59.1 SiO  6.0 SiO 0.91  1610 Amorphous * trace SiO 123  20      0.7 70 31 6 9 T        No. 42  3.8 MgO  1.0 MgO  -5.8 (1500 C.) (3 small peaks) MgO 32 197 29        86         16.6 Al2O3       1.7 Al2O3     Al2O3 1  1                                    24.6 SiO2      4.3 SiO2     SiO2 41  36        SMS(A) 35.9 SiO  1.1 SiO 0.78  1600 Amorphous SiO 159  42  0.75 148      176 10 10 T        No. 43  0.8 Al2O3   -0.4 (1500 C.) (No peaks) MgO 100 444 129 348             12.9 MgO       1.0 MgO     SiO2 185  177                                 51.2 SiO2      2.7 SiO2        SAS(C) 60.6 SiO  2.9 SiO 0.74  1600 Amorphous SiO 142  104  0.67 67 50        5 10 T        No. 44 20.7 Al2O3  1.0 Al2O3  -5.9 (7) (No peaks) Al2O3 7 167 7 133           22.6 SiO2       1.9 SiO2     SiO2 18  22                                  ACPS(A) 16.6      Al2O3  1.5 Al2O3 0.74  1600 Crystalline Al2O3 1  1  0.58 20 19 2 0 T           No. 45 39.0 CaO  6.2 CaO  -17.7 (Eut) (No glass) CaO 39 46 35 45           35.6 P2O5       2.2 P2O5     P2O5 #  #                                      6.7 SiO2      1.0 SiO2     SiO2 6  9        CMAS(A) 30.6 CaO  3.7 CaO 0.6  1530 Amorphous CaO 24  21  0.54 19 18 2        10 T        No. 46  5.9 MgO  1.0 MgO  -3.2 (Eut) (No peaks) MgO 10 40 7 39                41.6 Al2O3       2.8 Al2O3     Al2O3 2  2                             19.6 SiO2  2.2      SiO2     SiO2 4  9        SA 69.1 SiO  2.1 SiO 1.05 -10.7 1500 Crystalline (strong) * SiO 49      1155 125 1257 0.62 466 507 10 4 T        No. 47 32.2 Al2O3  1.0 Al2O3   (Eut) some glass (med) Al2O3 1106  1132        SW2A 21.3 CaO  1.0 CaO 0.78  1360 Amorphous CaO 70  65  0.66 127 140      10 10 W        No. 48 16.9 MgO       1.1 MgO  -0.2  (No peaks) MgO 91 322 116 369             1.1 Al2O3        Al2O3 10  1         61.5 SiO2       2.7 SiO2     SiO2 151  187                                  MAS(C) 34.9        MgO  3.5 MgO 0.73  1600 Amorphous (strong) * MgO 50  135  0.52 27 67 2        7 T        No. 49 25.5 Al2O3  1.0 Al2O3  0 (Eut) some cryst. (weak) Al2O3 2 58 2      144         41.7 SiO2       2.3 SiO2     SiO2 7  7                                      SAS(D) 60.3        SiO  3.6 SiO 0.84  1600 Amorphous * trace SiO 141  77  0.54 123 117 10        10 T        No. 50 16.5 Al2O3  1.0 Al2O3  -6.1 (7) (2 peaks) Al2O3 1 260 1 249            22.4 SiO2       2.3 SiO2     SiO2 118  171                               KMAS(A) 17.5      K2O       1.0 K2O 0.56  1500 Amorphous K2O #  #  0.94 6 7 1 10 T      No. 51 13.5 MgO       1.8 MgO  -2.4 (Eut) (No peaks) MgO 13 23 14 25            18.6 Al2O3      1.0 Al2O3     Al2O3 1  1         53.1 SiO2       4.8 SiO2     SiO2 9  10                                     KMAS(A)      20.0 K2O  1.5 K2O 0.54  1590 Amorphous K2O #  # 0.63 17 19 1 10 T              No. 52  9.0 Na2O  1.0 Na2O  -6.3 (Eut) (No peaks) Na2O # 31 # 49         33.8 Al2O3       2.3 Al2O3     Al2O3 14  32                                  39.9 SiO2      4.6 SiO2     SiO2 17  17 

We claim:
 1. A method of insulating an article comprising:(A) disposing on, in, near, or around the article thermal insulation which is a refractory insulating material having a maximum service temperature greater than 900° C. and comprising vitreous fibers having a composition comprising SiO₂, CaO, MgO, and optionally Al₂ O₃, wherein:(a) SiO₂ is present in an amount less than or equal to 71.24 percent by weight and (1) greater than 58% by weight SiO₂, if the amount of MgO in the composition is in the range 0 through 10 percent by weight; or (2) greater than the sum of (58+0.5(weight percent of MgO--10)) percent by weight SiO₂, if the amount of MgO in the composition is greater than 10 percent by weight; (b) greater than 0 and less than or equal to 42 percent by weight CaO; (c) greater than 0 and less than or equal to 31.33 percent by weight MgO; and (d) 0 to less than 3.97 percent by weight Al₂ O₃ ; wherein:the refractory insulation material has a maximum service temperature greater than 900° C.; the refractory insulation material has a shrinkage of less than 3.5 percent when exposed to a temperature of 1000° C. for 24 hours, and has a shrinkage of less than 3.5 percent when exposed to a temperature of 800° C. for 24 hours; and wherein the refractory insulation material is essentially free of alkali metal oxide and boron oxide fluxing components; and (B) exposing said insulated article to a temperature above around 900° C. for 24 hours.
 2. The method of claim 1, further comprising exposing said insulated article to a temperature above around 1000° C.
 3. The method of claim 1, wherein the amount of SiO₂ is less than 70 percent by weight.
 4. The method of claim 1, wherein the vitreous fibers crystallize as wollastonite, pseudowollastonite, or a mixture thereof after exposure to a temperature of 1000° C., and have the composition comprising:(a) 60 through 67 percent by weight SiO₂ ; (b) 26 through 35 percent by weight CaO; (c) 4 through 6 percent by weight MgO; and (d) 0 through 3.5 percent by weight Al₂ O₃.
 5. The method of claim 1, wherein the vitreous fibers comprise:(a) a maximum of 71.24 percent by weight SiO₂ ; (b) 4.46 through 34.49 percent by weight CaO; (c) 1.71 through 22.31 percent by weight MgO; and (d) 0 through 2.57 percent by weight Al₂ O₃.
 6. The method of claim 5, wherein the vitreous fibers further comprise:(e) 0 through 0.65 percent by weight Na₂ O; (f) 0 through 0.13 percent by weight K₂ O; (g) 0.08 through 0.4 percent by weight Fe₂ O₃ ; and (h) 0 through 1.23 percent by weight ZrO₂.
 7. The method of claim 1, further comprising forming said vitreous fibers into a bulk, blanket, block, or vacuum-formed form.
 8. The method of claim 7, wherein said vitreous fibers are formed into a needled blanket.
 9. The method of claim 1, wherein the vitreous fibers crystallize as diopside after exposure to a temperature of 1000° C., and have the composition comprising:(a) 60 through 64 percent by weight SiO₂ ; (b) 19 through 23 percent by weight CaO; (c) 14 through 17 percent by weight MgO; and (d) 0 through 3.5 percent by weight Al₂ O₃. 